Which ordered pair in the form (a, b) is a solution of this equation?
7a - 5b = 28

1. 0,4
2. 4,0
3. -3,-2
4. -2,-3

You can figure out the answer to this by plugging in each set of coordinates into the equation and solving.

7a - 5b = 28   Plug in the coordinates

1. 7(0) - 5(4) = 28   Multiply
     0   -  20  = 28   Subtract
         -20     ≠ 28

2. 7(4) - 5(0) = 28   Multiply
     28  -   0   = 28   Subtract
          28      = 28
 
3. 7(-3) - 5(-2) = 28   Multipy
     -21  -   -10  = 28   Simplify the double negative
     -21  +   10  = 28   Add
          -11        ≠ 28

4. 7(-2) - 5(-3) = 28   Multiply
     -14   - -15   = 28   Simplify the double negative
     -14   +  15  = 28   Add
             1        ≠ 28

As you can see, the only set of coordinates that worked was 2. (4, 0).