t is the input with years as the units. I is the output with dollars as the units. This is a function.
Work Step by Step
We know that t is the input because it is inside the parentheses. I is the output because it is the 'coefficient' of the parentheses. The units of years and dollars are both given in the problem. This is a function because for any number of years there can only be one corresponding amount of interest earned.