Answer:
Sales volumes                            <u>   $300,000  </u>    <u> $350,000 </u>     <u> $400,000</u>
Total selling expenses                <u>  $541,500  </u>    <u>  $595,750 </u>    <u>  $650,000 </u>
Explanation:
Basically, a flexible budget can be described as a budget that adjusts with changes in volume or activity. 
Therefore, monthly flexible selling expense budget for Cottonwood Company which adjusts with sales volumes can be prepared as follows:
Cottonwood Company
Monthly Flexible Selling Expense Budget
For the Month .....
<u>Details</u><u>                                                    $                      $                      $      </u>
Sales volumes                             <u>   300,000  </u>        <u> 350,000 </u>     <u> 400,000</u>
<u>Variable selling expenses:</u>
Sales comm. (6% of sales)                18,000              21,000           24,000
Shipping exp. (1% of sales)                 3,000               3,500             4,000
Misc. selling exp. (1.5% of sales)        4,500               5,250             6,000
<u>Fixed selling expenses:</u>
Sales manager's salary                  120,000            120,000         120,000
Advertising expense                       90,000             90,000           90,000
Misc. selling expense                <u>        6,000   </u>       <u>      6,000  </u>      <u>     6,000  </u>
Total selling expenses               <u>   541,500  </u>        <u>  595,750 </u>      <u>  650,000 </u>