1.2:x::14:42 =

To solve this proportion, we use the property that the product of the means is equal to the product of the extremes. In this case, we have 1.2 * 42 = 14 * x. Simplifying, we get 50.4 = 14x. To find the value of x, we divide both sides by 14, giving x = 50.4 / 14 = 3.6. Therefore, the correct answer is 3.6, which corresponds to option B. This means that the relationship between 1.2 and x is the same as the relationship between 14 and 42, following a proportional logic where the ratios are equivalent.