Given the following exponential function, identify whether the change represents growth or decay, and determine the percentage rate of increase or decrease per unit of xx, to the nearest tenth of a percent. y=7^{-x}

Atruck can be rented from company a $50 a day plus $0.60 per mile. company b charges $20 a day plus $0.80 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