The amount of paint required to paint a surface with an area of 50 m^2 is normally distributed with mean 6 L and standard deviation 0.3 L.
a. If 6.2 L of paint are available, what is the probability that the entire surface can be painted?
b. How much paint is needed so that the probability is 0.9 that the entire surface can be painted.
c. What must the standard deviation be so that the probability is 0.9 that 6.2 L of paint will be sufficient to paint the entire surface?