Find the dervative of 7x-6/y
With respect to what?
Are those both functions of some variable? Is y a function of x?
I'll assume for now that they are both functions of t.
Then $\displaystyle \frac{d}{dt} \left( 7x - \frac{6}{y} \right) = 7 \cdot \frac{dx}{dt} + \frac{6}{y^2} \cdot \frac{dy}{dt}$.
I hope that's what you're after.