You will need three roots for this, so we have
Let x = -30, -10 and +20
So the factors will be (x+30)(x+10)(x-20)
The divide it to 100, this will help bring the peak up and down
So the polynomial function R(x) will become
1/100 * (x+30)(x+10)(x-20)
R(x) = 1/100 * (x+30)(x+10)(x-20)
Finding the X-intercept:
Let R(x) = 0 and solve for x.
1/100 * (x+30)(x+10)(x-20) = 0
x = -30, -10, 20 are the x-intercepts.