Property: If x and y are positive, and \(0< x^2 < y^2\), then \(0< x < y\)

Given:
Quantity A: \(5 \sqrt{3x}\)
Quantity B: \(3 \sqrt{5x} \)

Square both quantities to get:
Quantity A: \((5 \sqrt{3x})^2\)
Quantity B: \((3 \sqrt{5x})^2\)

Simplify both quantities:
Quantity A: \((25)(3x)\)
Quantity B: \((9)(5x) \)

Simplify more:
Quantity A: \(75x\)
Quantity B: \(45x \)

Since we are told \(x > 0\), we can safely divide both quantities by x to get:
Quantity A: \(75\)
Quantity B: \(45 \)

Answer: A