#### Explanation:

Sowing you a slightly different approach with explanation of how we get there.

We end up with color(red)((106)/100xx$400) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $\textcolor{b l u e}{\text{This is how the final expression is derived}}$Percentage is just a fraction but a special one in that the bottom number (denominator) is always set at 100. So, as a fraction, all of something is $1 \times \text{ whatever it is"=>100/100xx" whatever it is}$So in this case we have all of the$400 + a bit of the $400 (100/100xx$400)+(6/100xx$400) Factoring out the$400 we have:

$400(100/100+6/100) ->color(red)($400xx106/100)color(blue)( = $424) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Trick for non calculator $400xx106/100 is the same as $400/100xx106 ->$4xx106=\$424