I need help starting this, I tried looking at examples but I can't get it...

The latest demand equation for you gaming website is given by q= -400x + 1200, where q is the number of users who log on per month and x is the log on fee you charge. Your IP provider charges you Site maintenance fee $20 per month and high volume access fee 0.5 per log on. Find the monthly cost as a function of the log on fee x. Find the monthly profit as a function of x. What is the largest possible monthly profit? What is the log on fee to obtain the largest possible profit?