How do you find the difference between median and mean

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 .

What are “like terms”? why can we only add like terms?

2y= 3 2 x−2 y = − 1 3 x + 1 y=− 3 1 x+1