ANSWER
D. 272.25 mm²
EXPLANATION
First we have to find the area of one face of one cube:
![A=2.75^2=7.5625\operatorname{mm}^2]()
Now we have to count how many faces of the squares are in the surface of the solid. Or a faster way is to multiply the total number of faces of the 9 cubes: 6*9=54 and subtract the number of faces that are not on the surface:
There are 18 faces of the cubes that are not on the surface of the solid. The number of faces from the 9 cubes that are on the surface of the solid is:
The surface area of the solid is the area of a face of one cube multiplied by the number of faces on the surface of the solid:
![SA=36\cdot A=36\cdot7.5625=272.25\operatorname{mm}^2]()