Answer:

Step-by-step explanation:
Given that,
The diameter of the cylinder, d = 8 cm
Radius, r = 4 cm
Height of the cylinder, h = 16.8 cm
We need to find the surface area of this cylinder. The formula for the surface area of the cylinder is given by :

So, the surface area of the cylinder is 
She needs to buy 1 more model car in order to have 4 rows of 6 model cars
9. Definitely 11
10. I'm pretty sure it's -6
As per the problem,
The larger pump takes 40 minutes to fill the pool.
The smaller one takes 60 minutes.
When both the pumps are working , let the time taken be x minutes , then we can write

Hence, when both the pumps works together, Time taken =24 minutes.