A certain product costs a company $\$65$ to make. The product is sold by a salesperson who earns a commission that is equal to 20% of the sales price of the product. The profit the company makes for each unit is equal to the sales price minus the combined cost of making the product and the commission. If the sales price of the product is $\$100$, which of the following equations gives the number of units, $u$, of the product the company sold to make a profit of $\$6,840$?