You could find the need of pine board by finding the perimeter of the frame. But first you need to equalize the units, because one of them is in feet and the other one is in inches.
18 inches = 18/12 feet
18 inches = 1.5 feet
perimeter = l + w + l + w
perimeter = 2 + 1.5 + 2 + 1.5
perimeter = 7
The perimeter is equal to 7 feet, therefore Carl needs 7 feet of pine board
