since the cost for hiring a plumber for three hours costs $120 so in graph A the graph has more likely stopped at $120 on the y axis which can be said as the cost axis too. I'm pretty sure the answer is A!
8x+12=p so you would take away 12 from p making the equation 8x=p-12 and then divide that by 8 so the equation is x= p-12/8 ( x equals p minus 12 over 8)