Answer:
$140
Explanation:
90-(3x10)-20+100= 140
He started with $90: (90)
Then he wrote 3 checks of $10 each: -(3x10)
Then he withdrew $20: -20
Finally, he made a deposit of $100: +100
Thus, our equation would be: 90-(3x10)-20+100=
(You might want to simplify this expression; giving you 140)