The difference of a number times 3 and 6 is equal to 7 . Use the variable w for the unknown number. The phrase a number uses the variable w. 3 times w is written as 3w The difference of 3w and 6 is written as 3w - 6 Set this equal to 7 3w - 6 = 7 This is our algebraic expression. To solve this equation for w, we type the algebraic expression into our search engine.