you have three points ... (0,3) , (1,9) , and (-2,15)Determine the equation (in standard form) of the parabola that has a y-intercept of 3, and that passes through the points (1,9) and (-2,15)

using the form , you can set up three equations ...

solve the system for the coefficients of the terms in the quadratic, a, b, and c.