A slow freight train chugs along a straight track. The distance it has traveled in miles after a hours is given by a function f(a). An engineer is walking along the top of the box cars at the rate of 3 miles per hour in the same direction as the train is moving. The speed of the man relative to the ground is OA. f(a) + 3. OB. f(x) + 3. Oc. f(x) - 3. OD. f'(a) - 3. In the answer box below, explain your reasoning for the choice you made above. Use complete sentences and correct grammar, spelling, and punctuation. Be specific and detailed. Write as if you were explaining the answer to someone else in class