(a) $T = 2\pi\sqrt{\frac{1}{MB_{H}}} \Rightarrow \frac{T_{1}}{T_{2}} = \sqrt{\frac{M_{2}}{M_{1}}} \Rightarrow \frac{M_{1}}{M_{2}} = \frac{T_{2}^{2}}{T_{1}^{2}} = \frac{(60/15)^{2}}{(60/10)^{2}} = \frac{4}{9}$
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