Rút gọn B

To simplify the given expression, we can group the terms in pairs:

(1+2) - (3+4) + (5+6) - (7+8) + (9+10) - (11+12) + ... + (299+300) + (301+302)

Within each pair, the sum is equal to 3. Therefore, we can rewrite the expression as:

3 - 3 + 3 - 3 + 3 - 3 + ... + 3 + 3

Since there are a total of 151 pairs (from 1 to 302), the expression simplifies to:

3 * 151

Therefore, B = 3 * 151 = 453.