Question 189151
It is better to place one question at a time if you want tutors to answer your questions here.

I will do number 3.

3) In a study, it was found that the threshold weight, W(h), defined as the weight above which the risk of death rises dramatically, is given by 

W(h)=( h/12.3)^3

Find the threshold weight for someone 5 ft 7 inches tall. 

There is a typo is your question. The threshold weight cannot be simply W.
The weight we need to find is defined as a fucntion and so what we need to find W(h), which is read "W of h."

To do so, replace h with 5 feet and 7 inches and simplify the cubic function using a calculator.

I will convert feet to inches for easy reading.

So, 5 feet = 60 inches.

Then 60 + 7 = 67 inches.

W(67 inches) = (67 inches/12.3)^3

W(67 inches) = (5.45)^3

W(67 inches) = 161.9

So, the threshold weight, according to your numbers, is 161.9