The cumulative distribution function of a random variable X

The cumulative distribution function of a random variable X is given by
F(x) =
   0          if x<1

       2/5       if 1 x< 2,
       3/20x+1/5    if 2 x < 4,
       9/10 ,             if 4 x < 6,
       11/10e^(6x),    if x 6.

(a) Find the largest number a < 7 such that P(a < X < 7) 1/4

(b) Find the smallest number b > 2 such that P(2 X b) 9/20.

Solution