Explanation:

We are given that x = 2×3×7×a = 42a and y = 2×2×8×b = 32b

We are given that the values of both x and y

lie between 120 and 130 (not including the two).

The only multiple of 42 in this range is 42×3=126

Hence, x=126

and a=3.
The only multiple of 32 in this range is 32×4=128

Hence, y=128

and b=4,

Hence, a−b = 3−4 = -1

Hence, option 4 is the correct answer.