Explanation:
It is given that,
Speed of Anna is x miles/hour
Speed of Sara is 10 mi/h
We need to find an expression that represents the average of Anna's and Sara's speeds. Average of two objects is given by :
![v=(v_1+v_2)/(2)](https://img.qammunity.org/2021/formulas/mathematics/high-school/3bgpw2mishphk4t1kiecdl2r99lgxgqrdu.png)
ATQ,
![v=(x+10)/(2)](https://img.qammunity.org/2021/formulas/mathematics/high-school/59jo18b0vmcuhvxwocv08zktvvdysey7e6.png)
The above expression represents the average speed of Anna and Sara.