M is the midpoint of JK. Find the coordinate of K.

J = (9, -5)
M = (5, -2)

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 .

You have 6 dollars +12 pennies +to quarters + 4 dimes=2 nickels how much do you have

How do you determine if an ordered pair is a solution to a given equation?