first off, let's recall that a cube is just 6 squares stacked up to each other, like in the picture below. Since we know its volume, we can find how long each side is.
part A)
![\bf \textit{volume of a cube}\\\\V=x^3~~\begin{cases}x=side\\[-0.5em]\hrulefill\\V=64\end{cases}\implies 64=x^3\implies \sqrt[3]{64}=x\implies 4=x](https://img.qammunity.org/2019/formulas/mathematics/middle-school/lqwq9dsfi4wldi3l15v2ze5vyaazs4mty2.png)
part B)
they have a painting with an area of 12 ft², will the painting fit flat against a side? Well, it can only fit flat if the sides of the painting are the same length or smaller than the sides of the crate, we know the crate is a 4x4x4, so are the painting's sides 4 or less?
![\bf \textit{area of a square}\\\\A=s^2~~\begin{cases}s=side\\[-0.5em]\hrulefill\\A=12\end{cases}\implies 12=s^2\implies √(12)=s\implies \stackrel{yes}{3.464\approx s}](https://img.qammunity.org/2019/formulas/mathematics/middle-school/zpzsu8q4nz9yg748vwtbsgqphzz00nwdez.png)