Stan and hilda can mow the lawn in 60 minutes if they work together. if hilda works twice as fast as stan, how long does it take stan to mow the lawn alone?

A) (S * H ) / (S + H) = 60
B) 2*H = S

Inserting "B" into "A"
(2H * H) / (2H + H) = 60
2H^2 = 120H + 60H
2H^2 -180 H = 0

H = 90 minutes
S = 180 minutes

Double Check
(180 * 90 ) / (180 + 90) = 60
Correct

Hilda takes 90 minutes Stan takes 180 minutes.