Let d=dollars and c=cents (what was actually in the envelope).
Anna says the envelope contains c dollars and d cents.
When 50c is removed from the envelope, the value remaining in cents is 100d+c-50. What’s left is twice as much as Anna said: 2(100c+d) cents.
Therefore 98d-199c=50, and d=(199c+50)/98.
If 3c+50=98, 3c=48, c=16.
So the envelope contained $33.16.