Question

The interest earned on money invested in a savings account is jointly proportional to
the amount initially invested and the length of time of the investment. If $250 is
invested for 2 years, it earns $25 in interest. Let I be the interest earned (in dollars), let
P be the dollar amount initially invested, and let t be the length of time of the
investment.
How much interest would be earned if $200 was invested for 3 years?

Answer 1

"The interest earned on money invested in a savings account is jointly proportional to
the amount initially invested and the length of time of the investment. "
That sentence, using the variables required, translates to:
I = Ptc where c is some constant we need to figure out. How do we figure out c?