Police use the function ​f(x)=\sqrt{20} to estimate the speed of a​ car, f(x), in miles per​ hour, based on the​ length, x, in feet of its skid marks upon sudden braking on a dry asphalt road. A motorist is involved in an accident. A police officer measures the​ car's skid marks to be 84.05 feet long. Estimate the speed at which the motorist was traveling before braking. If the posted speed limit is 50 miles per​ hour, and the motorist tells the officer he was not​ speeding, should the officer believe​ him? Please help me