For question a there would be 200 terms because the exponent only rises by 1 each time, but there is also a 1 at the beginning so it would be 199+1.
For question b, you divide 312 by 4 which would give you 78 terms. This is because the ending term is 319 and the starting term is 7, but since it didn’t start at 1, you had to subtract 319 from 7 to get 312, and then divide 312 by 4, because each term rises by 4.
For question c, you subtract 533 from 33, which would give you 500 terms. This is because it didn’t start at 0, so you have to subtract from the term it started on, which was 33.
I hope this helped.