Question 936434
You are given the definitions: {{{a * b = a -3b}}} and {{{a}}} # {{{b}}} ={{{ 2a + 3b}}}, 
looking at  the expression {{{(4 * 3)}}} # {{{5}}} and equation {{{a * b = a -3b}}}, we see that {{{a * b = (4 * 3)}}} ;so,   {{{a=4}}} and {{{b=3}}}

Let's use it:

{{{a * b = a -3b}}} ...........if  {{{ a=4}}} and {{{b=3}}}

{{{(4*3)=(4)-3(3)}}}, 

So, {{{(4*3)=-5}}}.

then   the expression {{{(4 * 3)}}} # {{{5}}}

{{{(4*3)}}}#{{{5}}}={{{(-5)}}}#{{{5}}}=> since given {{{a}}} # {{{b}}} ={{{ 2a + 3b}}}, then

{{{(-5)}}}#{{{5}}}= {{{2(-5)+3(5)}}}