一個求合的典型題目 煩請高人指點~

Q28:

For any positive integer n, the sum of the
first n positive integers equals [n(n+1)]/2. 
What is the sum of all the even integers between 99 and 301?

A.      10,100

B.      20,200

C.      22,650

D.     40,200

E.      45,150

Answer: