Here is my answer. Let just give assumptions. For example,the relationship is linear.Therefore the slope, "m," is the same throughout.
Let us make patrons the independent variable, the two points are: (1314, 11333) and (1544, 13518).
m = (13518-11333)/(1544-1314)
m = 9.5
profit = 9.5 patrons (you pick the variable names)
For 1 more patron substitute 1:
profit = 9.5 (1)
profit = 9.5
Isolate "patrons" and you get the function based on profit:
patrons = profit/9.5
The break even point is for 0 < profit.
0 < profit = 9.5 patrons
0 < 9.5 patrons
0 < patron