Does the X in math really represent that it value is still unknown?

Yes, but the X is only one of many variables that can be used to represent an unknown value. You can use any letter. though X is the most common.

the solution is h=10 because you add 9 to each side of the equation.

in problems involving proportions, we can use cross products to test whether two ratios are equal and form a proportion. to find the cross products of a proportion, we multiply the outer terms, called the extremes, and the middle terms, called the means.

hope it