Twice the sum of a number and 9 equals 7.

Use the variable y for the unknown number.

2 (y + 9) = 7 Since it says twice the SUM, you have to do the addition first so the 2 times goes outside the parenthesis.

2y + 18 = 7 Subtract 18 from both sides

2y = - 11 Divide both sides by 2

y = - 11/2