Acolony of 2^120 bacteria occupies a total volume of 1.3*10^15*m^3

The complete question is 
A colony of  2^120 bacteria occupies a total volume of 1.3 x 10^15 m^3. The surface area of a planet is approximately 5.42 x 10^14 m^2. 
Complete parts (a) and (b) below. 

a) Assume that the bacteria are distributed uniformly over the planet's surface. How deep would the bacterial layer be? (You can find the approximate depth by dividing the bacteria volume by the planet's surface area.) 
m 

b) Would the bacteria be knee-deep, more than knee-deep, or less than knee-deep? 

A. The bacteria would be less than knee-deep. 
B. The bacteria would be more than knee-deep. 
C. The bacteria would be knee-deep. 
D. It depends on the height of the person

Part a) 
Find the approximate depth 
= (bacteria volume / planet surface area) 
= (1.3 x 10^15 m³) / (5.42 x 10^14 m²) 
= 2.4 m 

the answer Part a) is 
2.4 m

Part b) 
No information is given about the height of the 'people' on this planet, and hence we cannot guess at their average knee height. 
2.4 meters is about 7.9 feet. That is obviously above the knee for any human, but. again, the question does not explicitly state that we are talking about Earth and humans

therefore

the answer part b) is the option
D. It depends on the height of the person

Ibelieve the answer would be 7, 13, 23

No i refuse to tell you the answer but the estimate is 10