A tank has inflow, outflow and stirring mechanism. Initially, the tank holds $500 \: L$ of a brine solution of concentration $200 \mathrm{~g} / \mathrm{L}$. At $t=0$, an inflow of another brine solution of concentration $100 \mathrm{~g} / \mathrm{L}$ starts entering the tank at the rate of $15 \mathrm{~L} /$ minute. At the same time the outflow of thoroughly stirred mixture also takes place at the same rate so that the volume of brine in the tank remains constant. The brine concentration $C(\mathrm{~g} / \mathrm{L})$ in the tank at any time $t$ (minute) can be expressed by the following differential equation
$$\frac{d C}{d t}+0.03 C=3$$
The brine concentration in the tank at $t=1.5$ hour is $\_\_\_\_\_\_ \: \mathrm{g/L}$. (rounded off to two decimal places)
