Two months ago, Wilson had a total of $150 in his bank account. Then last month, he deposited $17. A few days after, he made a withdrawal. This month, he deposited $21 so he has $16 more than what is in his account two months ago. How much did Wilson withdraw last month? Think carefully first, then make a decision:
Wilson had $150 + $17 = $167 two months ago before making a withdrawal. His money in his account now is $150 + $16 = $166. Since he deposited $21 this month, this means there was $166 - $21 = $145 last month after making a withdrawal. Therefore, Wilson withdrew $167 - $145 = $22. So, the answer is 22.