If you have two unknown quantities, then you need two equations
in order to find their values.
If there's only one equation, then the graph of that equation is a
straight line with no ends. EVERY POINT on that line is a pair of
numbers that can be the values of 'x' and 'y'.
(And I think you know how many points there are on a line.)
Here are a few correct answers to your question:
x = -10 , y = 26.5
x = -9 , y = 23
x = -8 , y = 19.5
x = -7 , y = 16
x = -6 , y = 12.5
x = -5 , y = 9
x = -4 , y = 5.5
x = -3 , y = 2
x = -2 , y = -1.5
x = -1 , y = -5
x = 0 , y = -8.5
x = 1 , y = -12
x = 2 , y = -15.5
x = 3 , y = -19
x = 4 , y = -22.5
x = 5 , y = -26
x = 6 , y = -29.5
x = 7 , y = -33
x = 8 , y = -36.5
x = 9 , y = -40
x = 10 , y = -43.5
Now, with those 21 correct answers out of the way,
there are only an infinite number of others.