Rectangle with the dimension: width (6b-2)in and length (4a+3)in. if a=.75 and b=.50, what is the perimeter of the rectangle?

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.