Here;
From the question we can assume QTY A > QTY B

let us assume 1.9 = 2 and 1.999 = 2

Now QTY A = \(2^3 = 8\)

and QTY B = \(2^2 =4\)

Moreover 1.999 will always be less than 2 , similarly 1.9 will always be less than 2

But cube root > square root.

If the question tells us compare between \((1.9)^2\) and \((1.999)^2\) then in this case \((1.999)^2 > (1.9)^2\). This is because the roots of both the QTY are same and 1.999 is more close to 2 than 1.9