You're on the right track. To find the number of groups, naturally, you would divide 98 by 6 ( 98/6). However, this does not give you a whole number. You'll have to choose a number close to 98 and is divisible by 6. That is either 96 or 102. I recommend using 96. Why? You will see that it fits the pattern given. 1 to 20th no. is the same as 1 to 98th no. in terms of calculation. So, the sum is (96/6)(8) + 2 + 1.
Try to calculate from 1 to 20th no. yourself. It follows the above calculation, (no. of groups) (sum of each group) + 2 + 1.

Thank you so much for your help:) i understand it

Sure np. :)