**Concept: The question tests on the basics of Arithmetic in the format of a word problem**

**Solution **

For the first 24 hours rent, the FIXED cost = x dollars

Hence the remaining 36-24 = 12 hours are billed @ y dollars/hour

=>VARIABLE Cost incurred = 12y dollar

=> Total cost incurred = Fixed Cost + Variable Cost

(x + 12 y )

**(OPTION A)**