Solve the proportion. 3/4=m/6

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 .

Find the difference (8ab+a+2) - (3ab+6)

Find the number of real number solutions for the equation. x2 + 5x + 7 = 0 0 cannot be determined 1 2