Need help with question 15 I did the work for it but the answer was wrong somehow it didn't work out question is on the photo

Answer:
336, (B)
Step-by-step explanation:
To find the surface area, find the area of each square and triangle
10x12 + 2(6x8)/2 + 12x6 + 8x12
This would then be,
120 + 48 + 72 + 96
Surface area = 336, (B)
You made a mistake on step 2.
When finding the area of triangle, you have to divide by 2.
Hope this helps!