If the rectangle has a fixed width of 300, it means that

where
and
are width and length, respetively.
So given the length
, the are would be

3 (k-12) = k-30
3k - 36 = k - 30
3k - k = -30 + 36
2k = 6
k = 3
The answer is
2
Explanation
You have to do 2/3 x 3 and you do that by multiplying 2 and 3 (6/6)
Which if you split up is 3/3, 3/3 = 2
334.54 + 198 = 532.54 grams total
hope this helps
It would be 41 because its m math