Probability of a call by walia = P(A) = 1/120                          ( 2 to 4 PM = 2 hours = 120 minutes)

Probability of a call by Sharma = P(B) = 1/45                            ( 2.30 to 3.15 = 45 minutes)

Probability of a call not made by Sharma on a particular minute = P(B') = 44/45

Now the entire time period for Mr Walia ( 2.0 to 4.0 pm) has three spans.

1) 2.0 to 2.30 PM                  2) 2.31 to 3.15 PM                             3) 3.15 to 4.00 PM

Probability of a call by walia in each period is-

 P(1) = 30/120 =1/4     P(2) = 45/120 = 3/8         P(3) = 45/120 = 3/8

Hence the probability of walia calls before sharma is -

 = probability of a call by walia in 1st period (2.00 to 2.30 PM) + probability in second span that Sharma doesn't make a call and walia makes one

                = P(1) + P(2 Ç B')

                = P(1) + [P(2) * P(B')]                                                          (As both the events are independent.)

                =(1/4)+[ (3/8)*44/45] =  (1/4) + (11/30)

                =37/60