Question

Thanks Remy.
I have one more -
2y + 9xy-4=0
I got -9y/2 + 9x

Answer 1

If you are trying to derive the equation for y,
y(2 + 9x) = 4
y = 4/(2 + 9x)

Answer 2

If you are looking for dy/dx, you could differentiate the equation I derived for y(x), or use implicit differentiation. In the latter case,
2 dy/dx + 9x dy/dx + 9y = 0
dy/dx (2 + 9x)= -9y
dy/dx = -9y/(2+9x)
That looks like what you got, but you shoul use parentheses to clarify what the denominator is