If 3rd term of an A.P. is 6 and 5th term of that A.P. is 12. Then find the 21st term of that A.P.

If 3rd term of an A.P. is 6 and 5th term of that A.P. is 12. Then find

1.	If 3rd term of an A.P. is 6 and 5th term of that A.P. is 12. Then find the 21st term of that A.P.
A.	40
B.	42
C.	60
D.	63
Answer» D.