A truck can be rented from Company A for $40 a day plus $0.70 per mile. Company B charges $20 a day plus $0.90 per mile to rent the same truck. Find the number of miles in a day at which the rental costs for Company A and Company B are the same.
Let the number of miles =M 40 + 0.70M =20 +0.90M, solve for M M = 100 miles - when the cost will be equal.