The function

is a parabola concave up, whose solutions are

from here, you can use the quadratic formula

to find that the solutions of the parabola are 
So, the parabola is positive if
(which wouldn't make sense in our case) or 
So, if Tanya caters 25 meals she breaks even, and starting with the 26th meal she will begin to profit.
What is the interquartile range of the data set? {48, 50, 65, 60, 80, 42, 45, 50, 42, 55, 45}
MissTica
Order the number:
42,42,45,45,48,50,50,55,60,65,80
Mean:50
Quartile 1:45
Quartile 3:60
60-45=15. As a result, the interquartile range is 15. Hope it help!