Final answer:
To find the constant of variation, divide the number of tests (27) by the number of hours (3), which results in a constant of 9 tests per hour.
Step-by-step explanation:
The question asks us to find the constant of variation, which in this context is the rate at which the teacher is grading tests. Given that the teacher grades 27 tests in 3 hours, we can calculate the constant of variation by dividing the number of tests by the number of hours. This will give us the rate of tests graded per hour.
Constant of variation (k) = Number of tests / Number of hours.
k = 27 tests / 3 hours = 9 tests per hour.
Therefore, the constant of variation is 9 tests per hour.