Answer:
Power, 
No of bulbs = 78400000
Explanation:
We have,
Water flows over Niagara Falls at the average rate of 2,400,000 kg/s, it mean it is mass per unit time i.e. m/t.
It falls from a height of 50 m
The gravitational potential energy of falling water is given by :
P = mgh
Power is equal to the work done divided by time taken. So,

So,

Let there are n bulbs that could power 15 W LED. It can be calculated by dividing the power by 15. So,

It means that the number of bulbs are 78400000.
(d) Density of Benzene: 0.8786 g/cm cubed
(m) Mass: 20.00g
Formula to solve (v) volume of benzene: V=m/d
V=20g / 0.8786g/cm cubed
Answer: Volume of benzene is: 22.8 cm cubed
Explanation: Well, density is mass divided volume. In this, it is what the volume is. All you need is mass divided by density. Hope this helps!