Use the inverse operation to isolate the variable. Undo the subtraction of 4 by adding 4 to both sides of the equation. –4 + 4 = 0, and 9 + 4 is 13. The solution is q = 13. Check the solution by substituting 13 for q in the original equation, and then simplify. 13 – 4 is 9 and 9 = 9 is a true statement, so 13 is the solution.
