I have nothing to add to the solution above, which is perfect, but with those answer choices, you don't actually need to do any work if you understand weighted averages reasonably well.

Average speed is a weighted average, weighted by the time spent at each speed. If you drive equal distances at 30 and at 60 miles per hour, you'll spend longer driving at 30 miles per hour. So the answer needs to be closer to 30 than to 60. Only A and B are possible, and A is way too small, so B needs to be right.