It is $82 for your profit
The number is -27 because 15 plus 12 is 27 snd you just add the negative
You did not provide a table however I used
x y
0 -1
3 1
(I tried to make a table above with x,y)
The x intercept is (3/2, 0)
The y intercept is (0, -1)
Slope 2/3
See pic for graph
3x3x3x3x3x3 which will give you your answer of 279