Answer
$x=0$
Work Step by Step
RECALL:
$(a+b)(c+d)=ac+ad+bc+bd$ (more popularly known as the FOIL method)
Use the FOIL method to obtain:
$(2x+5)(x-4)=(x+5)(2x-4)
\\2x(x) + 2x(-4)+5(x) + 5(-4)=x(2x)+x(-4)+5(2x)+(5)(-4)
\\2x^2-8x+5x-20=2x^2-4x+10x-20
\\2x^2-3x-20=2x^2+6x-20$
Put all the terms with a variable on the left side and the constants on the right side. Note that when you move a term from one side of the equation to the other, it changes to its opposite.
$2x^2-3x-2x^2-6x=-20+20
\\(2x^2-2x^2)+(-3x-6x)=0
\\0+(-9x)=0
\\-9x=0
\\\frac{-9x}{-9}=\frac{0}{-9}
\\x=0$