Question 843329
{{{w}}}= number of white shirts sold
{{{y}}}= number of yellow shirts sold
 
{{{w+y=30}}} because the store sold 30 sweatshirts.
{{{w+y=30}}} <---> {{{y=30-w}}}
 
{{{9.95w+13.5y=337.55}}} or {{{9.95w+13.5(30-w)=337.55}}}
because $337.55 worth of sweatshirts were sold.
 
{{{9.95w+13.5(30-w)=337.55}}}
{{{9.95w+13.5*30-13.5w=337.55}}}
{{{(9.95-13.5)w+13.5*30=337.55}}}
{{{-3.55w+405=337.55}}}
{{{-3.55w=337.55-405}}}
{{{-3.55w=-67.45}}}
{{{w=(-67.45)/(-3.55)}}}
{{{highlight(w=19)}}}
Going back to {{{y=30-w}}}
and substituting {{{w=19}}} we get
{{{y=30-19}}}
{{{highlight(y=11)}}}