Answer:
10%
Step-by-step explanation:
total loan = $25,000 x (1 - 3%) = $24,250
the present value of an annuity formula:
PV = annual payment x annuity factor
annuity factor = PV / annual payment = $24,250 / $3,188 = 7.607
the formula to calculate PV annuity factor is [1 - 1/(1 + i)ⁿ ] / i
7.607 = [1 - 1/(1 + i)¹⁵ ] / i
7.607i = 1 - 1/(1 + i)¹⁵
1/(1 + i)¹⁵ = 1 - 7.607i
1 / (1 - 7.607i) = (1 + i)¹⁵
after a lot of math:
i = 10%
1 / (1 - 0.7607) = 1.1¹⁵
4.18 = 4.18