If a is a real number, does the square root of a represent a real number?

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 .

If c(x) = 4x – 2 and d(x) = x2 + 5x, what is (cxd)(x)

What is 100,000 times 1/100,000, using the standard method of multiplication? write the answer as 10 to a power.