To simplify this expression, we can first multiply the two fractions and then simplify the resulting fraction.

(5/x - 4/y) * (3xy / 5y - 4x)

First, let's multiply the two fractions:

= (5(3xy) / x(5y)) - (4(3xy) / y(5y)) - (5(4x) / x(5y)) + (4(4x) / y(5y))
= (15xy / 5xy) - (12xy / 5y) - (20x / 5xy) + (16x / 5y)
= 3 - (12xy / 5y) - (20x / 5xy) + (16x / 5y)

Now, let's simplify by finding a common denominator:

= 3 - (12xy^2 / 5y^2) - (20x^2 / 5xy) + (16x^2 / 5y^2)

Finally, we can combine the terms:

= 3 - (12xy^2 + 20x^2) / (5y^2) + (16x^2) / 5y^2

So, the simplified expression is 3 - (12xy^2 + 20x^2) / (5y^2) + (16x^2) / 5y^2.