The question you are asking is Ex 3.2, 1 of Chapter 3 Class 10. Please check http://teachoo.com/1507/499/Ex-3.2--1---Form-pair-of-linear-equations-in-following-problems/category/Ex-3.2/
Teachoo is free. Login to view more pages.
Login with facebook
Login with gmail
On signing up you are confirming that you have read and agree to Terms of Service