Gretchen invested $1000 in a certificate of deposit that paid interest at a rate of 9% per year. How much was the CD worth at the end of the 3 years?

Iam trying to solve a linear equation for the shoe size of someone 84" tall taking into consideration example 1 is 69" tall with a shoe size of 9 and example 2 is 72 inches tall with a shoe size of 11. i understand that the equation should be y=mx+b and that on the graph the answer is (3,2) but i just don't understand how to create the equation to solve for 84-inches and 60-inches tall questions. after two days, i need .

How can you find the mean absolute deviation (mad) for this set of data?

Ithink i know it but i want to be sure so can you me out ?