Pharmacy A doctor's prescription calls for the creation of pills that contain 12 units of vitamin $\mathrm{B}_{12}$ and 12 units of vitamin E. Your pharmacy stocks two powders that can be used to make these pills: One contains $20 \%$ vitamin $\mathrm{B}_{12}$ and $30 \%$ vitamin $\mathrm{E}$, the other $40 \%$ vitamin $\mathrm{B}_{12}$ and $20 \%$ vitamin E. How many units of each powder should be mixed in each pill?