Answer:
45-gallons
Explanation:
Hideki is draining a 45-gallon aquarium at a rate of 15 gallons per minute.
Draining the gallons. So, rate should be negative because it reduce the amount of number of gallons.
Rate = 15 gallons per minute
Initial value = 45 gallons
Let t number of minutes aquarium left gallons.

This is linear function of given situation.
where, initial value is 45 and rate is 15
Hence, The initial value of the given situation is 45-gallons