Answer :
In order to calculate the number of units sold, we can use the formula below:
[tex]\text{Profit}=\text{ Revenue}-\text{ Cost}[/tex]The revenue is given by the earnings from selling the units, so using the variable x to represent the number of units sold, the revenue is given by 100x.
The cost is given by the fixed cost of $300 plus the variable cost of $20 per unit, so the total cost is given by 300 + 20x.
Now, writing the equation and solving it for x, we have:
[tex]\begin{gathered} P=R-C \\ 500=100x-(300+20x) \\ 500=100x-300-20x \\ 100x-20x=500+300 \\ 80x=800 \\ x=\frac{800}{80} \\ x=10 \end{gathered}[/tex]Therefore the number of units sold is 10.