21. 5 marks . The electoral popularity of a politician , in millions of votes t years after being elected varies according to f ( t ) = 20 for Ists 5 SE a ) What is the average rate of change in popularity berween I and 3 years after the election ? 6 ) using only the definition of the derivative ( and not formulas or tables of derivatives ) what is the instantaneous rate of chance of popularity 3 years after the election? Simplify your answers algebraically but do not evaluate them using a calculator ( no calculators allowed in exams ! )