I need help with 3 astronomy/math problems! Please help.?

[Ashley]

Solve the following problems:

16. Solve for the energy converted by fusing 800 kg of mass. The formula is E = mc2 where c = 2.99 * 108 m/sec-2.
- I know it is set up E=(800kg)(2.99x10^8m/sec^-2)

17. Solve for the period, p, of planet - moon system about one another if they have a semi-major axis of 0.025 AU. The formula is Ka3 = p2 where K = 1 year2 * AU-3.
-(1yr^2 x AU^-3)(.025AU)= p^2

18. Find for the velocity of a glowing body if a single wavelength of hydrogen, l (1) is measured in the lab is 656.3 nm and the same line of hydrogen, l (2), is measure in the body at 650.1 nm. The change in wavelength, Dl, equals the absolute value of l (1) - l (2). The speed of light, c = 2.99 * 108 m/s. The velocity, v = Dl*c/l(1).


Please help...