leading economic indictators: the value of the conference board index of 10 economic undicatators in the U.

leading economic indictators: the value of the conference board index of 10 economic undicatators in the U.S could be approximately by the following function of time t in months since the end of december 2002.if 6<t<15{ -0.2t + 119 if 15<t<20a) Estimate E(10), E(15, E(20)B)seketch the graph of E and use your graph to estimate when the index first reached 115