Surface Density of a Galaxy

The surface density of luminous matter in a galaxy has units of mass per area and obeys the equation

D(r)=D0er/r0,D(r) = D_0 e^{-r/r_0},

where D0D_0 is some constant with units of mass per area. Suppose we have some galaxy where D0=0.25 kg/mD_0 = 0.25 \text{ kg}/\text{m}. What is D(2r0)D(2r_0) in units of  kg/m \text{ kg}/\text{m}, to the nearest thousandth?

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