X is the number of levels. The rate of change is 7 minutes so that would all together would be presented as 7x. The y - intercept, or in this case the time already wasted setting up the game is 5 minutes. All together that would be 60 = 7x + 5. From there just use algebraic steps to find the number of levels you can reach in 60 minutes.
60 = 7x + 5
55 = 7x
7.86 = x
Since 0.86 isn't a whole level he could only finish 7 levels for free.
Hope this helps :)
