Point C is on the curve of equation y = (4-x)(x+5) so as you know the x co-ordinate you can simply sub it into the equation of the curve to find the y co-ordinate.
Additional Information: The curve of y=(4-x)(x+5) cuts the x-axis at A and B. A straight line cuts the curve at A and at C. The x-coordinate of C is 2. Find
(a) the coordinates of point C,
(b) the equation of line AC,
(c) the area of Triangle ABC
I am stuck at the (a) part. I can't find a solution to get the "y" of point C. I don't see any clue too. What should I do to get "y" of point C?