X + y = 15
5x - y = 9
Elimination method

(4, ? )

what number is the ?​

The ? Is 11.

You add the equations to get rid of one variable, then you have 6x=24 then you divide both sides and you have x=4, then you substitute the given value of x and you are left with 5*4 - y = 9. And the solution or well possible solution is y = 11 which gives yo. (x , y) = (4 , 11)

4 + y = 151
20 - y = 92

1*5
20 + 5y = 753

3 - 2
4y = 60
y = 15

the answer for (?) is 15
i’m not sure if this 100% correct but i’m trying my best to help you