Question 1070949
They mean for you to use {{{r}}} and {{{s}}} as your variables, like this:
{{{r}}}= number of red cars bought
{{{s}}}= number of silver cars bought.
The total number of cars bought is
{{{r+s=17}}} and that is one of your equations.
The other one deals with the amount spent buying those cars.
The {{{r}}} red cars costed ${{{7*r}}} .
The {{{s}}} silver cars bought costed ${{{5*s}}} .
The amount Alyssa spent buying all those cars was $111, so
{{{7r+5s=111}}} , and that is the other equation you need.
You need to solve the system of linear equations
{{{system(r+s=17,7r+5s=111)}}} <---> {{{system(s=17-r,7r+5s=111)}}}
but if you only need the value of {{{r}}} ,
substituting {{{17-r}}} for {{{s}}} in {{{7r+5s=111}}}
will give you an equation that you can solve for {{{r}}} :
{{{7r+5(17-r)=111}}}
{{{7r+85-5r=111}}}
{{{2r+85=111}}}
{{{2r=111-85}}}
{{{2r=26}}}
{{{r=26/2}}}
{{{highlight(r=13)}}}