CALLED resistance of that conductor. It is denoted by R.There are mainly two ways of the COMBINATION of resistances:1. Resistances in series:When two or more resistances are connected one after another such that the same current flows through them are called as resistances in series.The net resistance/equivalent resistance (R) of resistances in series is given by:Equivalent resistance, R = R1 + R22. Resistances in parallel:When the terminals of two or more resistances are connected at the same two points and the potential difference across them is equal is called resistances in parallel.The net resistance/equivalent resistance(R) of resistances in parallel is given by:\(\frac{1}{R} = \frac{1}{{{R_1}}} + \frac{1}{{{R_2}}}\)CALCULATION:Here 15 Ω and 60 Ω are in series combination, therefore the resultant resistance is⇒ R1 = 15 Ω + 60 Ω = 75 ΩHere 20 Ω and 30 Ω are in series combination, therefore the resultant resistance is⇒ R1 = 20 Ω + 30 Ω = 50 ΩNow 75 Ω and 50 Ω are in parallel, therefore the net resultant resistance is \(⇒ \frac{1}{R_{para}} = \frac{1}{{{75}}} + \frac{1}{{{50}}}=\frac{2+3}{150}=\frac{5}{150}=\frac{1}{30}\)⇒ Rpara = 30 Ω