Answer:
x = 40
Explanation:
First company:
Charges = per cubic foot of rock fee + delivery fee
y = $3.50x + $80
Second company:
Charges = per cubic foot of rock fee + delivery fee
y = $2.50x + $120
Equate the charges of both companies
$3.50x + $80 = $2.50x + $120
3.50x - 2.50x = 120 - 80
x = 40
The cost of the two companies, y are equal when x = 40