A=3 дм 4 см b=20 см c=4 дм S=?

To find the area (S) of a rectangle, we need to multiply its length by its width.

Given: a = 3 дм 4 см b = 20 см c = 4 дм

First, let's convert all the measurements to the same unit. 1 дм = 10 см

So, a = 3 дм * 10 см/дм + 4 см = 30 см + 4 см = 34 см c = 4 дм * 10 см/дм = 40 см

Now we can calculate the area (S): S = a * b

S = 34 см * 20 см = 680 см²

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