64 solid iron spheres each of radius x cm are melted to form a sphere with radius y cm .find ratio x: y

The last time i bought this product , it cost $20.00 but it looks like it cost 29. 60 today? what is the increase

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 .

Solve for x -2.3(r - 1.2 ) = -9.66 enter you answer as decimal.