Question 1018040
Parabola with horizontal SYMMETRY axis,  {{{x=a(y-k)^2+h}}};  if vertex is ON the y-axis, then h=0, and the form is {{{x=a(y-k)^2}}}.  


Next, your two given points on the parabola will give you the system of equations,
{{{system(a(4-k)^2=2,a(-2-k)^2=8)}}}


which you can work with...
{{{system(a=2/(4-k)^2,a=8/(2+k)^2)}}}


and then  {{{2/(4-k)^2=8/(2+k)^2}}} and solve for k, before solving for a.  That is HOW to continue.  You can finish this.