Step-by-step explanation:
Work of compressing a spring = 1/2 k x^2
where k is the spring constant and x is the displacement
For 2 cm displacement w = 1/2 k 2^2 = 2k joules
For 4 cm displacement , TOTAL work = 1/2 k 4^2 = 8k joules
but the work was already done compressing it to 2 cm...so subtract that amount from the total 8k - 2k = 6k joules
so work compressing from 0-2 is 2k joules
compressing from 2-4 cm is 6k joules more
or 3 times more as the original work