Sam currently has $48 in savings. He had been saving S6 each week. Yesterday he spent $90 of the savings. For how many weeks had he been saving?
(a) Write an equation that could be used to answer the question
above. First, choose the appropriate form. Then, fill in the blanks
with the numbers 48, 6, and 90. Let w represent the number of
weeks.

(b) Solve the equation in part (a) to find the number of weeks.
w = ?