Suppose that the original prism has length $\ell \mathrm{cm}$, width $w \mathrm{~cm}$, and height $h \mathrm{~cm}$. Since the volume of this prism is $12 \mathrm{~cm}^{3}$, then $\ell w h=12$. The new prism has length $2 \ell \mathrm{cm}$, width $2 w \mathrm{~cm}$, and height 3 cm. The volume of this prism, in $\mathrm{cm}^{3}$, is $(2 l) \times(2 w) \times(3 h)=2 \times 2 \times 3 \times l w h=12 \times 12=144$.