Answer:
82
Explanation:
let X = the number of hamburgers sold
let Y = the number of cheeseburgers sold a combined total of 328 were sold
so: X + Y = 328
cheeseburgers = 3 times the number of hamburgers sold
so: Y = 3X
substitute 3X into the equation for Y
X + 3X = 328
4X = 328
divide both sides by 4 to get the variable X by itself
X = 82
so: 82 hamburgers were sold Friday