"x", stands for a variable, in which any number can be placed inside. If there is an equal sign, x would stand for the number that solves the equation.
9(1 + 4x)
Simplify. Distribute 9 to both 1 and 4x
9(1) = 9, 4x(9) = 36x
36x + 9 is the same as 9(1 + 4x)
hope this helps
