A company determines that monthly sales S(t), in thousands of dollars, after t months of marketing a product is given by S(t)=313-6012+290t+140. a) Find S'(1), S'(3), and S'(4). b) Find S"(1), S''(3), and S''(4). c) Interpret the meaning of your answers to parts (a) and (b). (a) First, find S'(t). S'(t)=912-120t+290 S'(1)= (Simplify your answer.)