Answer:
10,000
Step-by-step explanation:
The combination consists of four digits, hence 0000 to 9999. There at 10^4 or 10,000 possible combinations (but only one that works).
now, there are 12 months in a year, so 18 months is really 18/12 of a year, thus
The answer is Flat Money
y = 4 + 3x
4 being the entrance cost and 3x being the 3 dollars per pound
