The total sales of S (in thousands of DVD's) of a certain movie are given by the following formula where t is the number of months since the release of the DVD. Use the formula to answer the questions. 7012 S(t)=2 +100 a) Find S'(t) 140001 S'(t)- (2100) b) Find S(20) and S'(20) The value of S(20) rounded to the nearest hundredth is Find f'(x) and find the equation of the line tangent to the graph of f at x = 1. f(x)=(1+4x)(5- 4x) f'(x) 32x+16 y-