The numbers Which are divisible by 7 and between 200 and 400 are:

203,210,217,................,399

Now first we find number of terms in this series

So

l=a + (n-1)*d     (a=first number, n number of termes and l=last number of the series) 

=>399 = 203 + (n-1)*7

=>399-203 = (n-1)*7

=>196 = (n-1)*7

=>n-1 = 196/7

=>n-1 = 28

=>n= 28+1

=>n = 29

Again sum of numbers are

Sum = (n/2)*(a+l)

        = (29/2)*(203+399)

        = (29*602)/2

        = 29*301  (when 602 and 2 is divided by 2)

        = 8729