The areas of the rectangles given in this problem are:
1. 21.
2. 4a.
3. mn.
What is the area of a rectangle?
The area of a rectangle of length l and width w is given by the multiplication of the dimensions, that is:
A = lw.
For this problem, each item gives the dimensions and we just have to find the areas, hence:
1. 7 x 3 = 21.
2. 4 x a = 4a.
3. m x n = mn.
More can be learned about the area of a rectangle at https://brainly.com/question/10489198
#SPJ1
