Answer:
[tex]\large \boxed{\text{64.2 g}}[/tex]
Explanation:
X + Y ⟶ XY
mass: 22.7 g x 86.9 g
According to the Law of Conservation of Mass, the mass of the product must equal the mass of the reactants.
[tex]\begin{array}{rcl}\text{22.7 g} + x & = & \text{86.9 g}\\x & = & \text{86.9 g} - \text{22.7 g}\\& = & \textbf{64.2 g}\\\end{array}\\\text{The mass of Y is $\large \boxed{\textbf{64.2 g}}$}[/tex]
