Tobey can mow a lawn in 50 minutes. working together, tobey and nick take only 30 minutes to mow the same lawn. how long would it take nick to mow the lawn alone?

Tobey=1/50 lawn per minute
tobey+nick=1/30 per minute
so therefor

1/50+nick=1/30
nick=1/30-1/50
nick=5/150-3/150
nick=2/150
nick=2/150 lawn per minute
so

2/150 tiems what=1
times 150/2 both sideds
what=75

75 mins

21, i'm pretty sure it's right lol