Answer:
a)The total amount of her  weekly stock sales  = $7,200
b) The total amount of her yearly stock sales  = $350,000
Step-by-step explanation:
(a)  Let us assume that the total a mount of her sales in a week  = $m
       Commission earned in a week = $288
       Now, 4 % of her total sales  = $288
       or, 4% of ($m)  = $288
     ⇒
      or, 
      ⇒ m = $7,200
Hence, the total amount of her  weekly stock sales  = $7,200
b)  Let us assume that the total amount of her sales in a year  = $k
      The total amount of commission earned  = $14,000
Now, 4 % of her total sales  = $14,000
       or, 4% of ($k)  = $14,000
     ⇒
      or, 
      ⇒ k = $350,000
Hence, the total amount of her yearly stock sales  = $350,000