Consider the differential equation y′ = .2(10 - y) from Example 6. If the initial temperature of the steel rod is 510°, the function f (t) = 10 + 500e^-0.2t is the solution of the differential equation. 

(a) Graph the function in the window [0, 30] by [-75, 550].

(b) In the home screen, compute .2(10 - f (5)) and compare this value with f′(5).