Alexa and Emily open up a lemonade stand in the front yard. They spent $10 for lemons, $5 for sugar and $3 for cups.  The lemonade is $4 a cup.  They sell a total of 21 cups.  How much profit did Alexa and Emily make after paying off expenses?
Alexa and Emily spend a total of $10 + $5 + $3 = $<<10+5+3=18>>18.
They make a total of $4 x 21 = $<<4*21=84>>84.
They make a profit of $84 - $18 = $<<84-18=66>>66.
#### 66