Algebra

First, let's note that

$3 + 4 + 5 = 3 *4$

$13 + 14 + 15 = 3 * 14$

This pattern will keep going. Thus, we just have

$3 [ 4 + 14 + 24 + ....... + 994 ]$

No. of terms =  100

Thus, our final answer is

$3 [ 994 + 4 ] [ 100 / 2 ] = 149,700$

Thanks! :)