In march tom had -£165 in his bank account. in april he had -£156. in which month did he have the least amount of money in his account?

March = -165
April = -156

In march he is negative MORE money, meaning he has MORE money in April

This question is trying to confuse you, ussually the lowest number means less, but these numbers are negative, so the lowest number means more.
He has the least amount of money in March