Use the pattern below to answer the question that follows.
302 = 300 + 2
304 = 300 + 4
306 = 300 + 6 : : :
400 = 300 + 100
If the sum of the first 50 even integers equals b, use the pattern above to select which of the following expressions represents the sum of the even integers x where 300 < x < 500.