We have to find the substraction of weight between white kitten and gray kitten, so:
[tex]\begin{gathered} \text{weight white kitten-weight gray kitten=4.05ounces-3.9ounces} \\ \text{weight white kitten-weight gray kitten=}0.15\text{ounces} \end{gathered}[/tex]The answer is 0.15 ounces.