Answer:
1314 cm^2.
Explanation:
Area of the 5 external surfaces
= 12*15 + 2*12*10 + 2*15*10
= 720 cm^2.
The dimensions of the internal surfaces are
12 -2, 15-2 and 10 - 1
= 10,13 and 9 cm.
So their area
= 10*13 + 2 * 9*10 + 2*9*13
= 544 cm^2
The area of the top edges
= 2*15*1 + 2* 10*1
= 50 cm^2
So the Total Surface area
= 50 + 544 + 720
= 1314 cm^2.