AHSME 1970 Problem 22

If the sum of the first $3n$ positive integers is $150$ more than the sum of the first $n$ positive integers, then the sum of the first $4n$ positive integers is $\text{(A) } 300 \text{(B) } 350 \text{(C) } 400 \text{(D) } 450 \text{(E) } 600$