Don't give me the answer, just explain how i can solve it, : solve: 13 - 3x = 4 (x - 2)

Sherrie is baking a pie for her family. she leaves the room and comes back to 35% of the pie having been eaten before she can put the topping on. how much 1 square inch strips of dough will she need for the top, now that a portion is missing? round your answer to the nearest while nimber.