Keys of a hash whose values sum to a particular value

I have a hash:

a = {"Q1"=>1, "Q2"=>2, "Q5"=>3, "Q8"=>3}

I want to retrieve a set of keys from it such that the sum of their values equals a certain number, for example 5. In such case, the output should be:

Q2 Q5

Please help me on how to get this.

def fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, tot)
  arr = h.to_a
  (href="https://forum.tuteehub.com/tag/1">1..arr.size).fihref="https://forum.tuteehub.com/tag/n">nd do |href="https://forum.tuteehub.com/tag/n">n|
    ehref="https://forum.tuteehub.com/tag/n">num = arr.combihref="https://forum.tuteehub.com/tag/n">natiohref="https://forum.tuteehub.com/tag/n">n(href="https://forum.tuteehub.com/tag/n">n).fihref="https://forum.tuteehub.com/tag/n">nd { |e| e.map(&:last).sum == tot }
    returhref="https://forum.tuteehub.com/tag/n">n ehref="https://forum.tuteehub.com/tag/n">num.map(&:first) uhref="https://forum.tuteehub.com/tag/n">nless ehref="https://forum.tuteehub.com/tag/n">num.href="https://forum.tuteehub.com/tag/n">nil?
  href="https://forum.tuteehub.com/tag/ehref="https://forum.tuteehub.com/tag/n">nd">ehref="https://forum.tuteehub.com/tag/n">nd
 href="https://forum.tuteehub.com/tag/ehref="https://forum.tuteehub.com/tag/n">nd">ehref="https://forum.tuteehub.com/tag/n">nd

h = {"Qhref="https://forum.tuteehub.com/tag/1">1"=>href="https://forum.tuteehub.com/tag/1">1, "Q2"=>2, "Qhref="https://forum.tuteehub.com/tag/5">5"=>3, "Q8"=>3}

fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, href="https://forum.tuteehub.com/tag/5">5)   #=> ["Q2", "Qhref="https://forum.tuteehub.com/tag/5">5"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, 2)   #=> ["Q2"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, 6)   #=> ["Qhref="https://forum.tuteehub.com/tag/5">5", "Q8"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, 4)   #=> ["Qhref="https://forum.tuteehub.com/tag/1">1", "Qhref="https://forum.tuteehub.com/tag/5">5"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, 8)   #=> ["Q2", "Qhref="https://forum.tuteehub.com/tag/5">5", "Q8"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, 9)   #=> ["Qhref="https://forum.tuteehub.com/tag/1">1", "Q2", "Qhref="https://forum.tuteehub.com/tag/5">5", "Q8"] 
fihref="https://forum.tuteehub.com/tag/n">nd_combo(h, href="https://forum.tuteehub.com/tag/1">10)  #=> href="https://forum.tuteehub.com/tag/n">nil 

Just out of curiosity:

hash = {"Q1"=>1, "Q2"=>2, "Q5"=>3, "Q8"=>3}
arr = hash.to_a

1.upto(hash.size).
  lazy.
  find do |i|
    res = arr.combination(i).find do |h|
      h.map(&:last).sum == 5
    end
    break res if res
  end.tap { |result| break result.to_h if result }  
#⇒ {"Q2" => 2, "Q5" => 3}