Working together Sarah and Heidi can milk the cows in 2 hour

Working together, Sarah and Heidi can milk the cows in 2 hours. If they work alone, it takes Heidi 3 hours longer than it takes Sarah. How long would it take Heidi to milk the cows alone?

Solution

2/s+2/h=1
h=s+3
h=6 Heidi alone in hours
s=3 Sarah alone in 3 hours