2 Answers: Choice A, Choice B
=================================================
Step-by-step explanation:
One painter charges $50 an hour. If they work for x hours, then they charge a total of 50x dollars.
For instance, let's say the painter works for x = 7 hours. This means s/he charges 50*x = 50*7 = 350 dollars overall.
That's for one painter. If we involve 3 painters, then the total bill comes to 50x+50x+50x = 150x dollars
We could also say 3*50x = 150x, since 3*(cost of one painter) = total cost for three painters.
This is why choices A and B are the two answers.
Choice C would be the answer if you only hired one painter. But instead, you hired three of them, so we can rule out choice C.
Choice D only works if x = 1 is plugged into 150x to get 150*x = 150*1 = 150. However, you don't want to limit yourself to this x value only. It's better to stick with 150x instead to be more general. That way you can find the cost for say x = 2 hours which is 150*x = 150*2 = 300 dollars. I'll let you try other x values.