Question

what rational number should be substracted from the sum of 3/14 and -4/7 to get 13 and 21

Answer 1

let the  number to be subtracted be x
so, 3/14 -4/7= -5/14.now, -5/14-x=13
                                         -x= 13 + 5/14
                                         -x= 
take out the LCm an d likewise you will get the value of x the same method you have to follow for 21 
hope it helps..