Find the 21st term: 19, 25, 31, 37 ...

43 because you add 6 to each one

Well because each term is increasing by 6 at a time, we just have to do that 20 times saying that 19 is the value of our 1st term. If we multiple 6 by 20 and add it to 19, we will get our 21st term. 6 times 20 is 120, if we add 19, it is 139.

139 is the 21st term.