Answer:
140
If that's wrong, try 147
Explanation:
With this brief sequence of numbers, we can see that the function is linear, and increases by 7 each term, with the first term at -21, and therefore, the "0th" term, or the y-intercept, at -28. With this information we can create a function in slope intercept form (y=mx+b):
,
where our m (slope) is 7, and our b (y-intercept) is -28.
If this doesn't make sense, then the easiest way is to just keep adding seven to the previous number until you get to the 24th term.
Hope this helps!