Question 962380
Let
c = # of cups of coffee sold
m = # of muffins sold
s = # of sandwiches sold

We know we sold 50 items, so this equation must hold:
{{{50=c+m+s}}}
We also know that we made $85, so this equation must also hold:
{{{85=c+2m+3s}}}
We know that we sold 5 more muffins than coffees, so we know that
{{{m=c+5}}}
If we substitute this, we get
{{{50=c+c+5+s}}}
{{{45=2c+s}}}
{{{s=45-2c}}}
Taking this equation, we substitute once again, this time into the second equation.
{{{85=c+2(c+5)+3(45-2c)}}}
{{{85=c+2c+10+135-6c}}}
{{{85=-3c+145}}}
{{{-60=-3c}}}
{{{c=20}}}
We now know that we sold 20 coffees. Since we sold 5 more muffins than coffees, we know we sold 25 muffins. Finally, since we sold 50 items in total, we discover that we sold 5 sandwiches.