[(150*151/2)-(49*50/2)]*2 = 20,200

We need the sum of positive numbers between 99 and 301. we can find the sum of numbers from 50 to 150 and multiply by 2.

since:

50*2 = 100 (the first positive number)

51*2 = 102 (the second positive number)

and so on

150*2 = 300 (the last positive number)

to find the sum of numbers from 50 to 150 we will use the given formula:

150*151/2 = the sum of all number from 0 to 150. subtract 49*50/2 or sum of numbers smaller then 50.

now multiply by 2 to get the sum of positive numbers from 100 up to 300.

the answer is (B)