A plumber needs four lengths of pipe, each 3 feet, 6 inches long. Pipes are sold by foot. How many feet does he need to buy?

Convert the pipe length to inches: 3 feet, 6 inches = 42 inches.
Multiply 42 inches by the number of pipes needed to find the number of inches of pipe needed: 42 × 4 = 168.
Divide the total amount of pipe needed in inches by 12 to determine how many feet of pipes are needed: 168 ÷ 12 = 14.