The equation is 4 = q + 13.

(Apply subtraction property of equality: If a = b, then )

4 – 13 = q + 13 – 13    (Subtract 13 from each side)

4 – 13 = q                     (Apply additive inverse property: 13 – 13 = 0)

4 = x                              (Subtract: 4 – 13 = – 9)

Check:

To check the solution substitute q = – 9 in original equation.

4 = – 9 + 13

4 = 4                             (Add: – 9 + 13 = 4)

The equality is true.

The value of q = – 9.