You have been called to testify as an expert witness in a trial involving a head-on collision. Car A weighs 1515 1b and was traveling eastward. Car B weighs 1125 1b and was traveling westward at 42.0 mph. The cars locked bumpers and slid eastward with their wheels locked for 17.5 ft before stopping. You have measured the coefficient of kinetic friction between the tires and the pavement to be 0.750. What speed u (in miles per hour) was car A traveling just before the collision? (This problem uses English units U = mph because they would be used in a U.S. legal proceeding.)