25.6
The question is asking for the difference between 4000 compounded interest and 4000 with simple interest.
So simply calculate 4000 compounded by 8% per annum for 2 years:
4000(1+0.08)^2=4665.6
Now calculate 4000 with simple interest of 8% per annum for 2 years:
4000(1+0.08×2)=4640.
Now subtract the simple interest amount from the compounded amount:
4665.6-4640=25.6
Hope that helps :)