Find the 2 numbers whose sum is 51 and whose difference is 13

2 #'s whose sum is 51: x + y = 51

2 #'s whose difference is 13: x - y = 13

add the 2 equations: 2x = 64 ⇒ x = 32

using either equation find y: 32 + y = 51 ⇒ y = 19

Answer the 2 #'s are 32 and 19