Make a sketch.
The area runs from x=-c to x=c.
If you simply integrate you will get 0 because the area is symmetric about the x axis.
It is also symmetric about the y axis.
To get the actual area (rather than the algebraic area), it will be 4 times the
integral from 0 to c of x2-c2 which will be a function of c.
Set that function equal to 470 and solve it.
If the function turns out to be a cubic, solve it graphically.