$${M = \frac{4 pi^2 a^3}{G T^2} \\ = \frac{4\pi^2 (1,42 \times 10^{14}\, \mathrm{m})^3}{(6,67 \times 10^(-11) \, \mathrm{N \cdot m^2 / kg^2}) [(15,2 a)(3,16 \times 10^7 \mathrm{s/a})]^2} \\ = \underline{\underline{7,35 \times 10^{36} \, \mathrm{kg}}}}$$