Suppose a random variableXhas a cumulative distribution function given by

F(a) = {0 for a<0, 1/2 for 0<=a<1, 3/5 for 1<=a<2, 4/5 for 2<=a<3,

9/10 for 3<=a<3.5, 1 for 3.5<=a.

a. Find the probability mass function forX.

b. Find the probability that a given observation of the value ofXis greater than or equal to 1.5.