RATIO of sand to gravel = 3 ∶ 4 = (3 × 3) ∶ (4 × 3) = 9 ∶ 12Ratio of gravel to CEMENT = 6 ∶ 7 = (6 × 2) ∶ (7 × 2) = 12 ∶ 14∴ Ratio of sand to cement = 9 ∶ 14