Final answer:
Bob needs to find the perimeter of the picture frame to determine how much wood he needs to purchase.
Step-by-step explanation:
Bob needs to find the perimeter of the picture frame in order to determine how much wood he needs to purchase. The perimeter is the distance around the frame, and it can be found by adding up the lengths of all the sides. If the frame has four sides of equal length, as is common in picture frames, Bob can simply multiply the length of one side by four to find the perimeter.