The first three steps for solving the quadratic equation by completing the square are shown. Fill in the missing number in the last step.
9x2 +54x = 7
9(x2 + 6x) = 7
9(x2 + 6x + 9) = 7 +.?
9x2 +54x = 7
9(x2 + 6x) = 7
9(x2 + 6x + 9) = 7 +.?