The formula for ending balance with simple interest is:

S = P(1 + rt)

where S = ending balance, P = principal, r = rate, t = time

1620.24 = P[1 + 0.08(9)] {substituted 1620.24 for ending balance, 0.08 for rate, and 9 for time}

1620.24 = P(1 + 0.72) {multiplied}

1620.24 = P(1.72) {added inside parentheses}

P = 942 {divided each side by 1.72}

**The principal was $942***- Algebra House*
**
**