Stan and hilda can mow the lawn in 30 min if they work together. if hilda works twice as fast as stan, how long does it take stan to mow the lawn alone?

Total Time = (Worker 1 * Worker 2) / (Worker 1 + Worker 2)
30 = (X*.5X) / (x + .5X)
30 = .5 X^2 / 1.5X
45 X = .5 X^2
Dividing both sides by X
45 = .5 X
X = 90
Stan will take 90 ,minutes and Hilda can do it in 45 minutes.
We can check this by putting the numbers in the formula:
30 = (45 * 90) / (45 + 90)
30 = 4,050 / 135
4,050 = 4,050
Answer is correct.