Answer:
On Tuesday, Devon took 30 dollars out of his checking account.
Explanation:
Starting with: $50 - Ending with $0
Monday: took out $20 or in other words -20 50-20=30
Tuesday: undetermined, but since that was his last day, it would correspond with $0 so, he must've took out $30 and then ended up with none in the end.
30-30=0
So, he took 30 dollars out on tuesday.