In triangles ABC and LMN draw the congruence marks

Explanation:

h = number of hours past 7 pm

20h = the number of glasses sold after h hours

20h+180 = adding on the 180 glasses already sold

20h+180 > 240 is the inequality to set up

Let's solve for h

20h+180 > 240

20h > 240-180

20h > 60

h > 60/20

h > 3

They must remain open more than 3 hours past 7 pm in order to sell more than 240 glasses of juice.

The earliest that they can close is 11 pm (since 4+7 = 11).

If h = 3, then

20h+180 = 20*3 + 180 = 240

meaning that they haven't reached their goal of getting over 240

So they have to stay open that extra hour to get past 240.