I'm assuming the two equations are as follows:
y = 5x
7x + 2y = -17
You can substitute 5x for y in the second equation since they are equivalent. Remember that whatever you do to one side you must do to the other as well.
7x + 2y = -17
7x + 2(5x) = -17
7x + 10x = -17
17x = -17
17x /17 = -17 /17
x = -1
Now we sub in the value we have for x to find y:
y = 5x
y = 5(-1)
y = -5
We now check that both answers are right by substituting them both into the second equation:
7x + 2y = -17
7(-1) + 2(-5) = -17
-7 + (-10) = -17
-17 = -17
And it looks like it works! So x = -1, and y = -5. Hope this helps! :)
