Question 751963
Assuming 90 marks is a score (and not a percentage)

R-right answers
W-wrong

Total questions: R+W=120

Score: R-0.25W=90


System

R+W=120
R-0.25W=90


Subtracting equations leads to

(R+W)-(R-0.25W)=120-90

then

1.25W=30

W=24

so that R=120-24=96


96 correct



:)