Find the product of: (x+3vs)(2x+3vs)

On a piece of paper graph y < 3x

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 .

Y=(x+3)(x-4)(x+1)^2 sulutions? multiplicity?