Answer:
D (he got 85% right which is more than 75%)
Step-by-step explanation:
because if you half 6/40 you get 3/20, now if you x by 5 you get 100 so do the same to the top (3x5 = 15)
Now you know that he got 15/100 = 15% wrong
so if you do 100 - 15 you get 85, so he got 85% right
85% is greater than 75% so therefore it is option D
hope this helps :)