Let m = the mass of the trash
Let V = original volume
The original density is m/V
After the volume is compressed, it is 0.35 of the original volume.
The mass remains the same, so the new density is
m/(0.35V) = 2.857V
The increase in original density is 2.857 = 285.7% (approximately 300%)
Answer: The density increases by a factor of 2.85 (or a factor of about 3)