
k = Kris' age 5 years ago
(2/3)k = Ben's age 5 years ago
k + 15 = Kris' age 10 years from now ← added 15 onto age 5 years ago
(2/3)k + 15 = Ben's age 10 years from now ← added 15 onto age 5 years ago
(2/3)k + 15 = (5/6)(k + 15) ← ten years from now, Ben will be 5/6 as old as Kris
4k + 90 = 5(k + 15) ← multiplied entire equation by 6, eliminating fractions
4k + 90 = 5k + 75 ← distributed
k = 15 ← subtracted 4k and 75
(2/3)k = 10 ← substituted 15 for k
Kris is 15
Ben is 10
 Proof
