If you would like to know how much time does Elke spend on the weights, you can calculate this using the following steps:
3/4 hour = 3/4 * 60 minutes = 45 minutes on the bikes
1/5 hour = 1/5 * 60 minutes = 12 minutes
12 minutes less than 45 minute: 45 - 12 = 33 minutes on the weights
The correct result would be 33 minutes.