Help with calculus problem? implicit differentiation

there's a problem that i dont understand at all... its asking for the implicit differentiation of a y' the problem is...

find y' if 3xy^2 - y + x = 7

please any help? thanks.........

3xy^2-y+x=7
take the derivative of both sides and set equal to each other by...

for the left side, first take the derivative of each term
(3x)(y^2) => 3x(2y y') + (3)(y^2) ... use the product rule to take the derivative of the first term

-y=> -y'

x=> 1
for the right side:
7=>0

so the derivative is:
3x(2y y')+(3)(y^2) -y' + 1=0

then it is algebra:

6xy(y') + 3y^2 - y' + 1 = 0

6xy(y') - y' = -3y^2 - 1

y' (6xy-1) = -3y^2 - 1

y' = (-3y^2-1) / (6xy-1)

because it is implicit you do not need to substitute anything for the y! (thats what you do for explicit)

here is a website that is very useful and will help you with calculus and other subjects:
http://www.khanacademy.org/#calculus

6xyy' + 3y² - y' + 1 = 0

solve for y'.