Let r be the percent annual interest rate of the account. Since $9000 are left for 5 years, for an outcome of $12,500, then:
Divide both sides by 9000:
Take the 5th root to both sides:
Use a calculator to find the decimal expression for r:
Therefore, to the nearest tenth:
This means that Joshua would need to invest his money on a 6.8% annual interest account.