if you are trying to solve for x simply solve for y=0. you will get three values of x in terms of a,b,c and d. refer to theory of equations . solve the following equations obtained by the theory:

x1+x2+x3=-b/a------------(1)

x1.x2+x2.x3+x3.x1=c/a----------(2)

x1.x2.x3=-d/a------------------(3)

where x1,x2,x3 are the 3 roots.also given that d=30 from the given point.