Answer:
a. Sales from January to June: Matrix B6
                              Hard    Soft       Plastic
San Francisco     3,600   7,200     11,400
Los Angeles        1,800    1,200      2,400
b) Ending Inventory: Matrix D:
                             Hard      Soft      Plastic
San Francisco      400     3,200     3,000
Los Angeles     2,800     8,400     3,200
Step-by-step explanation:
a) Data and Calculations:
Stock on January 1: Matrix A
                               Hard    Soft       Plastic
San Francisco       1,000   2,000    6,000
Los Angeles         1,000   6,000    2,000
Sales in January: Matrix B
                              Hard    Soft       Plastic
San Francisco       600     1,200     1,900
Los Angeles         300       200        400
Restocking: Matrix C
                            Hard    Soft       Plastic
San Francisco     500   1,400      1,400
Los Angeles       600      600       600
Total Sales over the first 6 months =
Matrix B * 6 = Matrix B6
Sales in January: Matrix B
                              Hard    Soft       Plastic
San Francisco       600     1,200     1,900
Los Angeles         300       200        400
* 6
= 
Sales from January to June: Matrix B6
                              Hard    Soft       Plastic
San Francisco     3,600   7,200     11,400
Los Angeles        1,800    1,200      2,400
Matrix C6 = Matrix C * 6
=
Restocking: Matrix C6
                            Hard     Soft       Plastic
San Francisco    3,000   8,400      8,400
Los Angeles      3,600   3,600      3,600
Inventory at the end of June =
Matrix A + Matrix C6 - Matrix B6
= Matrix D
Stock on January 1: Matrix A
                               Hard    Soft       Plastic
San Francisco       1,000   2,000    6,000
Los Angeles         1,000   6,000    2,000
+
Restocking: Matrix C6
                            Hard     Soft       Plastic
San Francisco    3,000   8,400      8,400
Los Angeles      3,600   3,600      3,600
-
Sales from January to June: Matrix B6
                              Hard    Soft       Plastic
San Francisco     3,600   7,200     11,400
Los Angeles        1,800    1,200      2,400
Ending Inventory: Matrix D:
                              Hard      Soft       Plastic
San Francisco      400     3,200     3,000
Los Angeles     2,800     8,400     3,200