[tex] 4(2x-5)[/tex] is equal to [tex]8x-20[/tex].
Because, when multiplying an integer with a bracket, you multiply the integer with all the stuff in it.
Like this,
[tex]a(bx+c)=\quad a\cdot bx+b\cdot c[/tex]
So if we expand the expression [tex]4(2x-5)[/tex]
[tex]4(2x-5)=\quad 4\cdot 2x+(4\cdot -5)\quad \Longrightarrow \quad 8x+(-20)\quad \Longrightarrow \quad 8x-20[/tex]