It is given Ms Rangel takes 3 minutes to grade one
and the time taken to get everything for grading is 5 minute.
The number of 3V's is 75.
as Ms Rangel takes 3 minutes to grade one, so she the time taken by her to grade 75 3V's is

and the total time taken by her to complete the work is

because she took 5 minutes for preparations.
so we can write this in the form of function f(t).
where t is the number of tests.

so this is the function we get.