Can someone break this down for me step by step? I'm reviewing for a midterm and got stuck on this problem.

5xy - 3x - 4 = 0

y' at (2,1)

I'm not sure where the 5 goes when you apply the product rule to the xy.

think of your equation as

(5x)(y) - 3x - 4 = 0

then the application of the product rule is more obvious

(5x)dy/dx + y(5) - 3 = 0
5x(dy/dx) = 3 - 5y
dy/dx = (3-5y)/(5x)

so at (2,1), dy/dx = (3-5)/10 = -1/5