Amateur radio practice exam question
The 15 metre band is 21 - 21.45 MHz, so the third harmonic will be above 63 MHz - too high. 10 Metres is 28 - 29.7 MHz, so the second harmonic will be 56 - 59.4MHz - looks like B is the right answer.

You have to look at the defined band frequency limits, rather than the frequency calculated from the band name.