Don't feel "I'm so bad at this question!" 90% of people do!.
Basically, what you are asking is this:
What interest rate will it take for $10,500 to grow to $35,000 in 12 years if it was compounded monthly? Well, your answer is=10.08%. But, how do we get that rate? Well, we use this foemula:
FV=PV [1 + R]^N, Where R=Interest rate per period, N=number of periods, PV=Present value, FV=Future value. So, we have:
35,000 =10,500[1 + R]^12*12 divide both sides by 10,500
3 1/3 =[1 + R]^144 take 1/144th root of both sides
1.00839597.. = 1 + R
R =1.00839597.. - 1
R=0.00839597 This is your interest rate month.
R=0.00839597 x 12 x 100
R=10.075% or 10.08% (rounded), your annual interest rate compounded monthly.