Doubt from HC Verma’s Concepts of Physics Volume I

If any one can explain step wise calculation of Example no. 17 of Chapter 2 of concepts of Physics by H C Verma Vol. 1.
Thanks in advance

Ans:

Solutions to the entire problems from concepts of Physics by HC Verma available at http://sites.google.com/site/physicsclassroomonline as well as www.plustwophysics.com