Calculus
posted by Jessi .
Which of the following is a point at which the tangent to y=(x2)^2(x+3) is horizontal?
a) (2,16)
b) (1, 18)
c) (1,4)
d) (2,0)
I found the derivative of y=(x2)^2(x+3)
which is 3x^22x8
if I solved for 0, it wouldn't give me the answer that are listed above. What did I do wrong?

dy/dx=3x^22x8 is good.
I get x=3/4 or x=2 for dy/dx=0.
So can you find the answer from above?