Concept:Add the same number to each term so the four numbers become proportional.Explanation:Let the required number be x.Then the numbers become 6+x, 14+x, 18+x, 38+x.For these to be in proportion, we set up: (6+x):(14+x)=(18+x):(38+x).That gives: 14+x6+x​=38+x18+x​.Cross-multiply: (6+x)(38+x)=(14+x)(18+x).Expand both sides: 228+44x+x2=252+32x+x2.Cancel x2: 228+44x=252+32x.Simplify: 44x−32x=252−228⟹12x=24⟹x=2.Thus, 2 is the least number to add.Answer:2