Answer:
Step-by-step explanation:
x = 4th number
y = sum of first three numbers
y = 76 + 78 + 81
y = 235
x = 85*4 - 235
x = 105
The sum of the 4 numbers is 85*4= 340. To get the other number, you do 340-(76+78+81) to get 340-235=105
ANSWER:340-235=105
