Question

5/7+1/14-1/21=.................

Answer 1

15+2-1/21
=16/21......

Answer 2

5/7 + 1/14 - 1/21
 l.c.m 7, 14 and 21 is 42
so, we have to make all the denominators as 42
* means multiplaication
5*6/7*6 + 1*3/14*3 - 1*2/21*2
30/42 + 3/42 - 2/42
30+3-2/42
31/42 

hope you got it 
mark it 5 star and mark as brainist