Answer:
The correct answer is for three hours they sold $ 2 ( x+l ); $ 2 ( y+m ); $ 2 ( z+n ) where x + y + z =15 and l + m + n = 9.
Explanation:
Haley had 15 boxes and Greg had 9 boxes of popcorn ready to be sold.
Price of each box is $2.
Let Haley sell x, y, z boxes per hour for 3 hours and Grey sell l, m, n boxes hourly.
Given x + y + z =15 and l + m + n = 9.
Amount worth sold by Haley in 1st hour is $2x.
Amount worth sold by Greg in 1st hour is $2l.
Amount sold in the 1st hour together is $ 2 ( x+l ).
Amount worth sold by Haley in 2nd hour is $2y.
Amount worth sold by Greg in 2nd hour is $2m.
Amount sold in the 2nd hour together is $ 2 ( y+m ).
Amount worth sold by Haley in 3rd hour is $2z.
Amount worth sold by Haley in 3rd hour is $2n.
Amount sold in the 3rd hour together is $ 2 ( z+n ).
Therefore amount earned hourly by selling popcorn together are $ 2 ( x+l ); $ 2 ( y+m ); $ 2 ( z+n ).