In this problem you are to make use of the formula P2 = (4(Π)2/μ)a3, together with the fact that μ = G(m1 + m2). Assume, as is approximately correct, that the semi-major axis for the Earth's orbit about the Sun is 93 million miles and that the period is 365 days. Also assume that the semi-major axis for the Moon's orbit about the Earth is 240 thousand miles and the period is 28 days.
Calculate the value of μ for the Earth-Sun System, the value of μ for the Moon-Earth system, and then,assuming that the mass of the Earth is negligible in the first system (ie that μ for the Sun is just G times the mass of the Sun) and the mass of the Moon is negligible in the second, estimate the ratio of the Sun's mass to the Earth's mass.
You can look up the values on the Internet to see that your results are reasonable, but the calculation is to be based on Kepler's Law as described above. If you do this correctly the result will be a fair approximation of the currently accepted value.