Carl is going to make a frame for a picture. the dimensions of the frame need to be 2 feet by 18 inches. how long must the board be that carl uses for his frame?

A rectangle has two pairs of sides of equal length. 

So perimeter P = 2ft + 18in + 2ft + 18in 

The units have to be all the same to add them so 

P = 2ft + 1.5ft + 2ft + 1.5 ft 

P = 7 ft. 

So the board would have to be 7 feet to make a 2ft x 1.5ft picture frame.