Hi everyone, quick question

Find dy/dx by differentiating implicitly and calculate its value with x=5, y=1

(x^2)-(xy^3)=20

This is what I did:

2x-3xy(dy/dx)=0

-3xy(dy/dx)=-2x

(-2x)/(-3xy)=dy/dx

2xy/3xy=dy/dx

2(5)/3(5)(1)=dy/dx

10/15=dy/dx

2/3=dy/dx

That answer is wrong. Where am I making the mistakes?

Thank you. Much appreciated.