I'll explain, since apparently the person above me doesn't believe in clarifying?
[PLAIN]http://img101.imageshack.us/img101/3676/step1a.gif
Since this equation is comprised of simple polynomials you will be able to differentiate each term by itself.
Using the power rule and remembering how to apply implicit differentiation via. the Chain Rule:
[PLAIN]http://img585.imageshack.us/img585/1932/step2a.gif becomes [PLAIN]http://img87.imageshack.us/img87/9609/step2b.gif
To differentiate a single x with a constant in front, it just becomes the constant due to the power rule, so 4x becomes 4.
Instead of using the quotient rule for -3/4x I would put (4x)^-1 on top and multiply that by -3, so that you can use the power rule instead (which is 99% of the time much easier to deal with).
(-1)*(-3) = 3 and then reduce the power by 1 and you end up with (3(4x)^-2) which can be rewritten as (3)/(4x^2).
The derivative of any constant is zero, 3 is a constant therefore you can just ignore it.
So far we have:
[PLAIN]http://img59.imageshack.us/img59/8198/step3.gif
So we can just solve for y' by dividing both sides by 10y, if we decided to maybe add fractions on the other side then clean things up with some algebra we get:
[PLAIN]http://img41.imageshack.us/img41/6554/step4.gif
So... apparently the answer you "know" ... is wrong? Wolfram Alpha agrees with me:
http://www.wolframalpha.com/input/?i=derivative+of+5y^2+%3D+4x+-+3%2F4x+%2B+3
Hope this helped!