Ok so we'll go ahead and solve for y first - we just need to get it alone on one side of the equal sign
Step 1: subtract 2x from each side
2x - 7y - 2x = 19 - 2x
This cancels out the 2x on the left, giving us
-7y = 19 - 2x
Step 2: divide both sides by -7
=
+
This gives us
y = -19/7 + 2x/7
That should be your answer for the first question. Now solving the next parts are easy. All you need to do is plug in x.
When x = -3
y = -19/7 + 2x/7
y = -19/7 + 2(-3)/7
y = -19/7 - 6/7
y = -25/7
When x = 0
y = -19/7 + 2x/7
y = -19/7 + 2(0)/7
y = -19/7
When x = 3
y = -19/7 + 2x/7
y = -19/7 + 2(3)/7
y = -19/7 + 6/7
y = -13/7
Hope that helps! Feel free to ask if I can help with anything else :)