need help with 3 questions??

The power P that can be obtained from a windmill is directly proportional to the cube of the wind speed s.

(a) Write an equation that expresses this variation. (Use k for the constant of proportionality.)

The pressure P of a sample gas is directly proportional to the temperature T and inversely proportional to the volume V.

(a) Write an equation that expresses this variation. (Use k for the constant of proportionality.)

The rate r at which a disease spreads in a population of size P is jointly proportional to the number x of infected people and the number P − x who are not infected. An infection erupts in a small town with population P = 9000.

(a) Write an equation that expresses r as a function of x. (Use k for the constant of proportionality and P for the population.)

b) Compare the rate of spread of this infection when 30 people are infected to the rate of spread when 1100 people are infected. Which rate is larger? By what factor? (Round your answer to one decimal place.)

The infection rate when 1100 people are infected is about....... times smaller\bigger than when 30 people are infected.

(c) Calculate the rate of spread when the entire population is infected.