Answer:
The answer is 12 + 3 - x
Explanation:
The keywords are "and" and "difference". "And" means adding and "difference" means subtracting. And if the phrase says/or writes a number before any keywords that represent an operation then, it means that number comes first before the sign or operation.
Hope I'm correct as this is the first time I am answering a question and I don't have a pen and paper with me right now XD.