f(x)=2x and g(x)=5x^2-2x+4..stuck on step c. to find the (g*f)(x) and part d. too.

Question

Hi..I am working on this problem..already figured out the first two parts of the problem.

f(x)=2x and g(x)=5x^2-2x+4..stuck on step c. to find the (g*f)(x).

a. (f*g)(x)..the answer was  10x^2 - 4x +8

b. (f*g)(-3)= 25

now this part c. is what I am stuck on....(g*f)(x) = 

and then I have to do part d. and part of that problem is from part c. 

d. (g*f)(-4)

Answer 1

a) (f○g)(x)=f(g(x))=f(5x²-2x+4)=10x²-4x+8, so you were right!

b) (f○g)(-3)=f(g(-3))=f(55)=110, not 25. (g(-3)=5(9)-2(-3)+4=45+6+4=55.)

c) (g○f)(x)=g(f(x))=g(2x)=5(2x)²-2(2x)+4=20x²-4x+4.

d) (g○f)(-4)=320+16+4=340.