12. 1.14 Prompt: $x=250 \times \frac{(1+0.05)^{50} \times 0.05}{(1+0.05)^{50}-1}=13.69$ yuan/year, $\frac{x}{12}=$
$$
\frac{13.69}{12}=1.14
$$
12. For a residential building, the construction investment is 250 yuan per square meter, considering a lifespan of 50 years, and an annual interest rate of $5 \%$, then the monthly rent per square meter should be $\qquad$ yuan to recover the entire investment.