Algebra

x+3(x-6)=2x-3

x+3x-18=2x-3

    4x-18=2x-3   |-2x

    2x-18=   -3    |+18

    2x     =   15   | : 2

      x     =   7,5

$\begin{array}{rll}x+3(x-6)&=&2x-3\\ x+3x-18&=&2x-3\\ 4x-18&=&2x-3\\ 4x-2x&=&18-3\\ 2x&=&15\\ x&=&\dfrac{15}{2}\end{array}$