Final answer:
The correct way to find the total number of students is option B: 10 x 5 + 9.
Step-by-step explanation:
To find the total number of students in Sarah's after-school club, we need to multiply the number of groups by the number of students in each group.
In this case, there are 5 groups and each group has 9 students.
So the total number of students is 5 x 9 = 45.
Therefore, the correct way to find the total number of students is option B: 10 x 5 + 9.