Let f(x)=7x^3 −2x−12 and g(x)=−3x^3 -8x^2 +10x . what is the function rule for (f+g)(x) ? a.(f+g)(x)=4x^6 −8x^2 +8x−12 b.(f+g)(x)=4x^3 −12x^2 +8x−12 c.(f+g)(x)=4x^3−8x^2+8x−12 d.(f+g)(x)=4x^6−8x^2+12x−12