Answer:
13
Explanation:
We have been given that mean = 21 and total number of hours = 8
Let the number of prescriptions filled during hour two be x
![Mean = \frac{Sum\hspace{3}of\hspace{3}all\hspace{3}the\hspace{3}number\hspace{3}of \hspace{3}prescriptions}{Total\hspace{3}number\hspace{3}of\hspace{3}hours}](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v9wzy5p9mrhqdwz4iyvfv6nttjgadt2z5a.png)
![21 = (18+x+22+25+16+24+22+28)/(8)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/93rbnhtpp5jfogae7yv1etgqruagtn4p8y.png)
![21 = (155+x)/(8)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/243en3mpv801i4hcd53lz6o6yrm7t7iifg.png)
Multiply both sides by 8
![21 * 8= (155+x)/(8)*8](https://img.qammunity.org/2020/formulas/mathematics/middle-school/755ruoy5ag4e9mtkft550cjfbllbsdm4ub.png)
Cancel out the 8's on the top and bottom of the right side
![168= 155+x](https://img.qammunity.org/2020/formulas/mathematics/middle-school/34cm17djaolms5qqfesytcpy8pa4lcacdt.png)
Subtract 155 from both side
168-155=155+x-155
Cancel out +155 and -155 from the right side
13 = x
Flip the sides
x = 13
So, the number of prescriptions filled during hour two = 13