<human>:  To get to the library, Jill spends 12 minutes waiting for her first bus, 30 minutes riding on her first bus, and half the combined wait and trip time on her second bus. How many minutes does her second bus ride take?
<bot>: How many minutes does Jill spend waiting for and riding the first bus? ** First add the time spent waiting for the first bus to the time spent on it: 12 minutes + 30 minutes = <<12+30=42>>42 minutes
How many minutes does Jill spend on the second bus? ** Then divide that time by 2 to find the time she spends on the second bus: 42 minutes / 2 = <<42/2=21>>21 minutes
#### 21