Answer:
7x
Step-by-step explanation:

Let's Solve :
Therefore, the correct answer is 12
_____________________________

Answer:
22.5
Step-by-step explanation:
8hrs=220
1hr=220÷8
1hr=22.5
Answer:
The sum of ages of all 18 pupils in the class = 81
Step-by-step explanation:
Total number of pupil in the class = 18
Average of years in the class = 
Now, 
⇒Average of sum of ages in the class = 4.05
Let us assume the sum of ages of all students in the class = m
By the formula for AVERAGE:


or, m = 18 x 4.5 = 81
Hence, the sum of ages of all 18 pupils in the class = 81