There shouldn't be a negative in front of one of the equations.
Well he probably likes you and if you like him tell him, but make sure he isn’t playing you and you are ok with dating first. If you don’t like him and he likes you let him down nicely cause you don’t wanna be rude. All the signs are there, so do what ever pleases you.
I believe it would be B. linear because it would depend on how much of a decrease the monthly rate changes and based on that the five hundred would change per every dollar (new customers=500x+5000) x being $decrease in monthly rate