Answer:
The expression representing total number of juice boxes they bought is

Explanation:
Given:
Number of 6-packages of juice bought by Jamar = 8
Number of 6-packages of juice bought by grandmother = 3
We need to write an expression which models Total number of juice boxes they bought.
Solution:
Let the Total number of juice boxes they bought be represented by 'y'.
Also Let number of boxes in each package be 'x'.
1 package = x boxes
6 package = number of boxes in 6 package.
By using Unitary method we get;
number of boxes in 6 package =

Now we can say that;
Total number of juice boxes they bought will be equal to sum of Number of 6-packages of juice bought by Jamar multiplied by number of boxes in 6 package plus Number of 6-packages of juice bought by grandmother multiplied by number of boxes in 6 package.
framing in equation form we get;

Hence the expression representing total number of juice boxes they bought is
