Hello!
Part (a):
To obtain the amount of time spent to serve each customer, we can use the formula below:
[tex]\text{time for each customer}=\frac{\text{total time}}{\text{ number of customers}}[/tex]
Let's check these three situations:
[tex]\begin{gathered} t=\frac{12}{4}=3 \\ \\ t=\frac{21}{7}=3 \\ \\ t=\frac{27}{9}=3 \end{gathered}[/tex]
It appears to take the same amount of time to serve each customer (3 mins each one).
Time to serve 10 customers: 10 * 3 = 30 minutes.
Part (b):
We will solve it in a similar way, but now using this formula:
[tex]p=\frac{\text{ number of points}}{\text{ dollars spent}}[/tex]
Let's check each option:
[tex]\begin{gathered} p=\frac{24}{3}=8 \\ \\ p=\frac{40}{5}=8 \\ \\ p=\frac{63}{9}=7 \end{gathered}[/tex]
Each dollar spent does not always earn the same number of points.