You can split thus shape into 3 different rectangles.
The bottom rectangles area can be calculated using Base x Height
So 8 x 12 = 96cm²
The middle triangle is a little more difficult. but all you need to do is find the base to do base times height. You do this by doing 8 - 4 (because the length below it is 8 and you just minus 4)
8-4 = 4
So now you do 4 x height (5)
20cm²
Third top rectangle now.
Look at the bottom length and just minus that by 4 and 2 because if you imagine the bottom length coming up you can see it would be cut off.
So 8 -4 -2 = 2
The bottom is 2 (we know this is correct as the top length is also 2)
Base x Height
2 x 6 = 12cm²
Now add all the area together
96 + 20 + 12 = 128cm²