(12дм+3800мм)

To start solving this expression, we need to ensure all units are the same. For simplicity, we can convert everything into meters (м).

We know that:

• 1 дм (decimeter) is equal to 0.1 м (meters)
• 1 мм (millimeter) is equal to 0.001 м (meters)

First, we need to convert 12 дм to meters: 12 дм * 0.1 м/дм = 1.2 м

Next, convert 3800 мм to meters: 3800 мм * 0.001 м/мм = 3.8 м

Now adding the two quantities together: 1.2 м + 3.8 м = 5 м

So, the expression (12дм + 3800мм) equals 5 meters.