6. [-/0.31 Points] DETAILS The displacement (in meters) of a particle moving in a straight line is given by s = t - 4t + 15, where t is measured in seconds. (a) Find the average velocity over each time interval. (1) [3, 4] m/s [3.5, 4] m/s (lii) [4, 5] m/s (iv) [4, 4.5] m/s (b) Find the instantaneous velocity when t = 4. Show your work by completing the four-step process. (Simplify your answers completely for each step.) 5 = f(t) = 13 - 4t + 15 Step 1: f( 4 + h ) = Step 2: f( 4 + h ) - f ( 4 ) = (Hint: Factor completely.) Step 3: f ( 4 + h ) - f(4 ) h Step 4: f' (4) = lim f(4 + h) - f(4) h - 0 h m/s