Answer:
(4 , -3)
Explanation:
Put "y" by itself on one side to isolate it
3x - y = 15
3x = 15 + y
3x - 15 = y
Substitute "y" in the second equation for "3x - 15"
x + (3x - 15) = 1
4x - 15 = 1
4x = 16
x = 4
Then, plug 4 into x in any of the equations
4 + y = 1
y = -3
(4 , -3)