Answer:
x = -3 and y = 6
Explanation:
by plugging the function (y = 3x + 15) into the y value in the function (3x + 3y = 9), you can then solve to find that x = -3
After solving for the x-value, plug -3 into the easiest equation to solve for the y-value (y = 3x + 15) to then find that y = 6
This is method of solving is called substitution