-x^2 +3x +4=-(x+1)(x-4)...parabola that go down
tu get area, integrate
?????? wanna integrate from x=-1 tu x=+4 ????
integral=-(1/3)x^3 +(3/2)x^2 +4x
at x=4, integral=+18.6666666...
at x=-1, integral=-2.166666666
integral from -1 tu 4=18.666 -(-2.1666)=20.83266