A plot of land doubles in size by adding x metered to the length and x meters to the width of the land. If the original plot had an area of 200 by adding 300 meters, what is the value of x

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.