Answer:
12.51%
Step-by-step explanation:
after the first 6 years, you will have:
FV = PV (1 + r)ⁿ
FV = $8,500 (1 + 6%)⁶ = $12,057.41
If you need to have $19,320 in 4 years, then you must determine r:
$19,320 = $12,057.41 (1 + r)⁴
$19,320 / $12,057.41 = (1 + r)⁴
1.6023 = (1 + r)⁴
⁴√1.6023 = 1 + r
1.1251 = 1 + r
1.1251 - 1 = r
0.1251 = r
r = 12.51%