Simple interest can be modeled with the equation A = P(1 + rt).
For your problem, we can simplify this a bit to
N = P x R x T
Which just means principal x rate x time
First, let's figure out what interest rate we're getting. We can use our equation to solve for that by substituting each variable with the known amount:
75 = 6000 x R x 1
That simplifies to:
75 = 6,000 x R
0.0125 = R
( Or 1.25%)
To calculate the interest for a new principal, just plug the new numbers into the same equation:
N = 10,500 x 0.0125 x 1
N = $131.25
