HELP! please. very urgent. precal.

ok here are some questions i need help with ASAP.

1)express this using rational exponents: 5 times the square root of 81x^(3)y^(8) (theres also a little 4 above the beginning of the radical.)

2)a scientist has 37 grams of a radioactive substance that decays exponentially. assuming k= -0.3, how many grams of radioactive substance remain after 9 days? round your answer to the nearest hundredth.

3) solve using common logarithms: 4^(x-3)=7^x

4)what interest rate is required for an investment with continuously compounded interest to double in 8 years?