Ruby is deciding between two truck rental companies. company a charges an initial fee of $70 for the rental plus $2.50 per mile driven. company b charges an initial fee of $90 for the rental plus $1.50 per mile driven. let a(x)a(x) represent the amount company a would charge if ruby drives xx miles, and let b(x)b(x) represent the amount company b would charge if ruby drives xx miles. write the equation for each function and determine which company would be cheaper if ruby needs to drive 15 miles with the rented truck.