The surface area of bigger cube is:
\(4\times10\times10=400\left(cm^2\right)\)
The surface area of small cube is:
\(4\times1\times1=4\left(cm^2\right)\)
The area of a face of small cube is:
\(1\times1=1\left(cm^2\right)\)
Because the surface area of the soild is calculate more twice times the area of a face of small cube. So the surface area of the soild is:
\(400+4-1\times2=402\left(cm^2\right)\).