Your grades in the three tests in College Algebra are 87, 59 and 73.

Calculation:

Let x = the final test grade

Average of four grades = 75

Therefore, \(\frac{87+59+73+x}{4}=75\)

\(\frac{219+x}{4}=75\)

\(219 +x = 300\)

\(x=81\)

Hence, the final test grade is 81.

Calculation:

Let x = the final test grade

Average of four grades = 75

Therefore, \(\frac{87+59+73+x}{4}=75\)

\(\frac{219+x}{4}=75\)

\(219 +x = 300\)

\(x=81\)

Hence, the final test grade is 81.