A=3 дм 4 см b=20см c= 4 дм S=?

To find the area, we need to multiply the length and width of the rectangle.

Given: a = 3 dm 4 cm b = 20 cm c = 4 dm

First, let's convert all the measurements to the same unit, centimeters.

1 decimeter (dm) = 10 centimeters (cm)

a = 3 dm * 10 cm/dm + 4 cm = 30 cm + 4 cm = 34 cm c = 4 dm * 10 cm/dm = 40 cm

Now we have: a = 34 cm b = 20 cm c = 40 cm

The area of the rectangle is given by:

S = a * b = 34 cm * 20 cm = 680 cm^2

Therefore, the area of the rectangle is 680 square centimeters.