Hey,
If we look at the series we notice that the odd numbers are added to the preceding number to get the next number,
that is,
3+5=8
8+7=15
15+9=24
therefore,
24+11=35
35+13=48
48+15=63
63+17=80
and so on...
thus this is the required answer to the question.
I hope this helps.
All the best!
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