Question

3x+y=12 and 4-y=9 solve xy

Answer 1

add the 2 equations to eliminate y
solve for x
then plug this value of x into one of the original equations and solve for y.

Answer 2

are you sure you have the 2nd equation right?

its not 4x - y = 9?

Answer 3

if its is correct then you can find y from this equation and plug the result straight into equation 1 to find x.

Answer 4

I have same thought. answer will be easy then. but anyway method to solve is same in either case.