Don't understand how to do multi step equation integers with word problems

Use the x-intercept method to find all real solutions of the equation.x^3-10x^2+27x-18=0

Monica build a remote control toy airplane for science project to test the plane she launched it from the top of a building the plane travel a horizontal distance of 50 feet before landing on the ground a quadratic function which models the height of the plane in feet relative to the ground at a horizontal distance of x feet from the building is shown

For f(x)=2x+3 and g(x)=x^2- 8 find (f+g) (x)