Answer: 312m
Don't forget the units!
Explanation:
To find the surface aria, you use the 3 numbers to find the aria of each surface, then add up all the numbers you found.
Let's start by finding the right face (12 by 3). From your picture, we can tell its 12m long, and 3m tall. To find the aria of any face, we multiply the length, times the width.
12 x 3 = 36.
Now let's look at where it says 8m. Since that face is just as tall as the first one, we can tell its 3m tall.
8 x 3 = 24.
We can continue this for the top face.
Since the width of the second face we did is 8m, and the width of the first one is 12m, we can tell that the top one is 8 x 12. (96).
We can do this again for the other 3 sides.
A shortcut i like to take, is to do 3 of the sides, (Like the ones we did) and add them together, then double the sum.
36+24+96=156.
156x2=312.
This shortcut should work, because by adding the aria of half the sides together, we get exactly half the answer.
When doing this, it only works to do 3 different sides. it will not work if you do the same side twice, or a parallel side.
I encourage you to let me know if this method works for you! I hope this helps!