8 + 9 x 3 - 4
Use BODMAS. This is a basic rule for math which means:-
Brackets Open Division Multiply Addition Subtraction
In the equation written above you multiply first as it comes first in BODMAS, then add and finally subtract.
It goes like this :-
8 + 9 x 3 - 4
8 + 27 - 4
35 - 4
= 31
31 is your answer.
Hope this helps!