Can someone help me with this geometry volume question ty

Hunter designs two flags for his adventure club. what is the length of the base, x, of the larger flag? enter your answer, as a decimal, in the box.

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 .

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.