Question 900626
Can you first make the system?  Three points, each give an equation; and you know this is as {{{x=ay^2+by+c}}} because the symmetry axis is given as horizontal.  Use the general equation as {{{ay^2+by+c=x}}}.


Use each point to make a separate equation and then simplify as necessary.  That will be your system of equations to solve.  The variables you are solving are the coefficients a, b, and c.