1. average of the data 12, 24, 20, 28

average formula :

a = total sum / number of item

a = 12 + 24 + 20 + 28 / 4

a = 84 / 4

a = 21

the average of the data is 21

2. surface area of a cube formula :

sa = 6a²

sa = 6(9)²

sa = 6(81)

sa = 486cm²

the surface area of the cube is 486cm²

3. the formula of area of :

a. square = edge x edge (or a²)

b. rectangle = length x width (or l x w)

c. triangle = base x height / 2 (or b x t / 2)

4. area of the triangle :

we can use the formula of an area of a triangle :

a = b x t / 2

a = 12 x 13 / 2

a = 78cm²

the area is 78cm²

perimeter of the triangle :

to find the perimeter of the triangle, we can just add up the edge of the triangle.

p = 12 + 14 + 14

p = 40cm

the perimeter is 40cm