In Problem, what is the probability that a household will use more than 400 gallons of water per day?

Problem:-
In a certain city, the daily use of water (in hundreds of gallons) per household is a continuous random variable with probability density function

Find the probability that a household chosen at random will use

(A) At most 400 gallons of water per day (B) Between 300 and 600 gallons of water per day.