In this question, the ratio 7:2:4 alone doesn't give us any absolute quantities, but they are in equal proportion, so we can think of each as multiplied by an integer n. Therefore, since the total is 520, we can write
7n + 2n + 4n = 520
13n = 520
n = 40
The difference between the number from England and from Japan will be 7n − 4n = 3n = 3(40) = 120.
The correct answer is (A).