Alternate method :

difference of first series = 4, difference of second series =5

so difference of common series will be always LCM (4,5 )= 20 .

by seeing both series ...we can easly find first term = 21,

and last term of common series will be less than or equal to 417 ,bcoz common series will go up to common of both and first sequence is till 417 .

series like 21 ,41,61.... 401....(bcoz 401%20=1 ,)

so 401= 21+ (n-1)20

380/20= (n-1)

**n= 20** hence answe is 3)