Complete the table of solutions
7x-2y =-21
X Y (X,Y)
3 ---- (---- , ----)
----- 0 (---,---)
I am not sure what you are doing... but
if your first value is x=3 then
7(3) -2y = -21
21 -2y = -21
-2y = -42
y = 2
Do the same thing for 0, but replace your y with the "0"