Question

How do you do simple intrest?

Answer 1

i = p*r*t, where:

i is the interest earned, a dollar amount
p is the principal, the original dollar amount
r is the interest rate, expressed as a decimal fractin
t is the number of years.

Best that you post an actual problem, work on it and ask for feedback if need be.

Answer 2

Use the simple interest formula: A = P(1 + rt)