Chapter 6.2, Problem 26E

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

     $f\left(t\right)=\{\begin{array}{cc}.15e^{-.15t}& ifx\ge 0\\ 0& \text{otherwise}\end{array}$

Find the probability that a household chosen at random will use

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