Let's suppose the diameter (AB) of the circle is 20 cm and AD is 18 cm. How would we calculate DC? Or for that matter, is it possible to calculate angle CBD or angle CAD?

This is much easier when you use a software like MS Excel. You have to list the points first. These are: (1,3), (2,2.5), (3,4), (4,5), (5,6.5), (6,5.5), (7,7), (8,6), (9,7.5), (10,7) and (11,9).

Do a scatter plot for this points and add a trend line and you obtain the equation of the line fit. The equation is p=0.6m+2.4

We use this equation to find p when m=12.

p = (0.6×12)+2.4
p = 9.6

Total profit in month 12 would be 9.6 thousand.