To find the length of side DE in triangle DEF, we can use the property of similar triangles.
Since triangles ΔABC and ΔDEF are similar, the ratios of the corresponding sides are equal. This means:
\[ \frac{AB}{DE} = \frac{AC}{DF} \]
We know:
- AB = 16
- AC = 12
- DF = 3
We can substitute these values into the ratio:
\[ \frac{16}{DE} = \frac{12}{3} \]
Calculating the right side:
\[ \frac{12}{3} = 4 \]
Now we have:
\[ \frac{16}{DE} = 4 \]
To find DE, we can cross-multiply:
\[ 16 = 4 \cdot DE \]
Now, solve for DE:
\[ DE = \frac{16}{4} = 4 \]
Thus, the length of DE is 4.