This problem is an example of when we need to take a weighted average. We simply can't just find the average of 5 and 8, because there are different children of each each.
To start, lets multiply the total number of children by their individual ages.
6 x 5 = 30 years 14 x 8 = 112 years
There are 142 years among the 20 years, so divide 142 by 20. This gives us an average age of 7.1 years.
Count the units on the sides. On the Y axis the rectangle is 4 units and on the X axis the rectangle is 6 units. Area of a rectangle=L*W so, 6*4=24. Perimeter is 4*2 and 6*2=8+12=20. Hope this helps!