Step-by-step explanation:
Add up the four test scores (80, 95, 85, x) then divide by 4 and set that result equal to 88. The equation you get is (80+95+85+x)/4 = 88. Now solve for x.
(80+95+85+x)/4 = 88
(260+x)/4 = 88
4*(260+x)/4 = 4*88
260+x = 352
x+260 = 352
x+260-260 = 352-260
x = 92
The fourth missing number is 92
