Hello! AP Calc student here. Compound interest is simply a matter of knowing the equation and how you use it to achieve what the problem is asking of you.
Compound interest is expressed as this equation: A = P(1 + r/n)^n•t
I remember having a problem remembering each variable, but essentially, A is the final amount, P is the original amount owed, r is the interest rate, n is the amount of times compounded, and t is the time elapsed.
A = amount owed(what you are finding in the problem)
P = 3500
r = 14% (expressed as .14)
n = t (compounded each year)
t = time in years
So, for both a and b, you just plug in the relevant variables in the context of the problem and solve for A!
a) A = 3500(1 + .14/1)^(1•1)
b) A = 3500(1 + .14/2)^(2•2)