I=$26.24, P=$500, T=18 months the annual interest rate is

A = $2,861.60

I = A - P = $2,361.60

Equation:
A = P(1 + rt)

Calculation:
First, converting R percent to r a decimal
r = R/100 = 26.24%/100 = 0.2624 per year.

Solving our equation:
A = 500(1 + (0.2624 × 18)) = 2861.6
A = $2,861.60

The total amount accrued, principal plus interest, from simple interest on a principal of $500.00 at a rate of 26.24% per year for 18 years is $2,861.60.