Hey there! :)
You have to find the area of ALL of them and add it together.
Let's start with the 3 rectangles
Formula = l × w
6 × 3 = 18
6 × 4 = 24
6 × 5 = 30
Now, the 2 triangles
Formula = (b × h) ÷ 2
Both triangles are the same:
(5 × 2) ÷ 2 = 10 ÷ 2 = 5
(5 × 2) ÷ 2 = 10 ÷ 2 = 5
Add all of them
18 + 24 + 30 + 5 + 5 = 82
The surface area = 82 cm²
Hope this helps :)