I am confused on how to solve this problem :

$5000 is invested for 4 years at 7% per annum compound interest.

a. what will the amount be at the end of this period?
b. what is the expression for the value of the investment after n full years?
c. the investment will exceed $10,000 after n full years. what is an inequality that represents this information? what is the value of n?

The formula that i have learned for this isn't working for me and i don't know how to do this.

a. The fomula you should be using, for a four year period of deposit, is
Final value = (Initial value)*(1.07)^4
b. Replace "4" with the number of years "n" for other lengths of time
c. 5000*(1.07)^n > 10,000
(1.07)^n > 2
n log 1.07 > log 2
n > 10.24 years

thanks