If 60 seconds are in a minute, 60 minutes are in an hour, and 24 hours in a day then 86400 seconds are in a day what type of reasoning is this

Darcy deposited $390 into a savings account. as long as the account balance remains at or above $150, she does not have to pay a service fee for the account. for how many months can she withdraw $40 a month without having to pay service fees? a) 3 b) 5 c) 6 d) 9