Actuarial solution please!

A large pension fund has a value of 500,000,000 at the start of the year. During the year the fund receives contributions of 100,000,000, pays out benefits of 40,000,000 and has interest income of 60,000,000. Estimate the yield rate on the fund for each of the following circumstances: Contributions, benefits and interest are uniformly spread throughout the year. Benefits and interest are uniformly spread throughout the year and the contributions are made in one lump-sum at time (i) t =0, t=1/4 t = 1/2 t = 3/5,or t=1