To find the density of the toy, we need to use the formula for density, which is:
\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]
We have the mass of the toy which is given as 25 grams. Next, we need to calculate the volume of the rectangular pyramid.
The formula for the volume \( V \) of a pyramid is:
\[ V = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
First, we calculate the base area of the rectangular base:
\[ \text{Base Area} = \text{Length} \times \text{Width} = 4 , \text{cm} \times 5 , \text{cm} = 20 , \text{cm}^2 \]
Now we can calculate the volume of the pyramid:
\[ V = \frac{1}{3} \times 20 , \text{cm}^2 \times 6 , \text{cm} = \frac{1}{3} \times 120 , \text{cm}^3 = 40 , \text{cm}^3 \]
Now that we have the volume, we can calculate the density:
\[ \text{Density} = \frac{25 , \text{grams}}{40 , \text{cm}^3} = 0.625 , \text{g/cm}^3 \]
Thus, the density of the toy is:
\[ \boxed{0.625} , \text{g/cm}^3 \]