===== Answer =====

It will take 42 minutes to fix all the buses.

|            ^  Bus Repair Time  ^^^ Total Time ^
^  Worker A  |  30  |  12  |     |  42  |
^  Worker B  |  23  |  18  |     |  41  |
^  Worker C  |  14  |  17  |  8  |  39  |