Amount for compound interest, A = P(1 + r)ⁿ
P= Principal = 70600, r = rate = 4.2% per year = 0.042, n = number of years = 3.
A = P(1 + r)ⁿ
A = 70600(1 + 0.042)³
A = 70600(1.042)³ use calculator
A ≈ 79874.45
Interest = Amount - Principal = 79874.45 - 70600 = 9274.45
d. final balance: $79,874.45 interest earned: $9274.45
Option d is the answer.