Ireally don't understand my teacher , can anyone here me out

Let x specify the number of 16 ounce serving

If you buy the mug you acquire the first serving including the mug.

So the price of x is:

295 + 50(x - 1)

the x - 1 here shows that the first serving with the mug.

And then count the whole thing in cents.

The fee of throwaway cups is 85x

So breakeven is computed by:

295 + 50(x - 1) = 85x

295 + 50x - 50 = 85x

245 = 35x

x = 245/35 = 7

Checking this will give us:

mug 2.95 + 50*6 = 5.95

disposable

8.5*7 = 5.95

So the answer is D.