Problem Solving (PS) | For any positive integer n, the sum of the first n positive multiples

For any positive integer n, the sum of the first n positive multiples of 3 equals 3n(n + 1)/2. What is the sum of all the multiples of 3 between 299 and 601 ?

A. 15,150
B. 22,275
C. 45,000
D. 45,450
E. 90,900

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