Oh thanks!
So means 5 marks if both sci n math correct? Tats why minus the 3?!

The difference mark for science and mathematics
If mathematics correct = 5
If science correct = 3
The difference between math and science
= 5 - 3
= 2

This is assumption method.
Assumed all science questions answer correctly
Total mark = 25 × 3 = 75
Short fall = 107 - 75 = 32
These shortfall mark must be come from Mathematics mark.
As we already count 3 marks for all questions (science), these 32 marks should be from math questions 2 marks more from each math question answer correctly.
2 marks → 1 questions
32 marks → 16 questions.

Either science or mathematics answer correctly.
If science answer correctly = +3
If mathematics answer correctly = +5

Actually, you can use guess and check for P4.
25 questions
If 13 mathematics and 12 science answer correctly
Total marks
= 13×5 + 12×3
= 65 + 36
= 101 X

If 14 mathematics and 11 science answer correctly
Total marks
= 14×5 + 11×3
= 70 + 33
= 103 X

If 15 mathematics and 10 science answer correctly
Total marks
= 15×5 + 10×3
= 75 + 30
= 105 X

If 16 mathematics and 9 science answer correctly
Total marks
= 16×5 + 9×3
= 80 + 27
= 107 ✔️

Mathematic questions correctly = 16

Oh okie okie! I got it now! Thanks for ur help!

Really appreciate ur time to work it out! ✨

Welcome. Hope your can use assumption method in the future. It save time! (^_^)