An electrician cuts a 21 ft piece of wire into two pieces. One piece is 13 ft longer than the shorter piece. How long are the pieces?

X = longer piece, y = shorter piece

x + y = 21

x = y + 13

y + 13 + y = 21

2y + 13 = 21

2y = 21 - 13

2y = 8

y = 8/2

y = 4 < = = = shorter piece is 4 ft

x = y + 13

x = 4 + 13

x = 17 < = = longer piece is 17 ft