An equation of the line normal to the graph of y = (3x^2 + 2x)^.5 at (2,4) is

a) -4x + y =20

b) 4x + 7y = 20

c) -7x + 4y = 2

d) 7x + 4y = 30

e) 4x + 7x = 36

so i know you have to get the derivative, which I found to be (3x+1) / (sqrt[3x+2])

but now what do i do