APR=7%, monthly interest rate, i=7%/12=0.07/12
Monthly payment, A=100
After 4 years, n=4*12 = 48 months,
the balance F is therefore
F = A((1+i)^n-1)/i
=100((1+0.07/12)^48-1)/(0.07/12)
=5520.92
Answer: the balance after 4 years at APR=7% with monthly payment of $100 is $5520.92 to the nearest cent.