Hi i need some help with these probability

Question 4 (10 marks) The amount of time in hours that a computer functions before breaking down is a continuous random variable with probability density function (pdf) given by where c is a constant. (a) Find c such that )3; (at) is a valid pdf. (b) What is the probability that a computer will function between 50 and 150 hours before breaking down? (c) Find E[X), the expected value of X