What is the solution of the system? {2x+y=15 {x−y=3

We could use substitution method to solve the problem since it's much easier on this system.

First, we need to change x to the value of y. Use the second equation.
x - y = 3
x = 3 + y

Second, subtitute 3 + y to the x in the first equation
2x + y = 15
2(3 + y) + y = 15
6 + 2y + y = 15
6 + 3y = 15
3y = 15 - 6
3y = 9
y = 3

Third, we already found y, now subtitute 3 to y in the first equation to find the value of x
x = 3 + y
x = 3 + 3
x = 6

The solution = (6,3)
x = 6
y = 3

The answer would be the second choice : )