Answer:
C. 36 in.
Explanation:
The wall is 66 inches high by 72 inches wide.
The tiles are
a) 9 inch square = 3 by 3
b) 16 inch square = 4 by 4
c) 36 inch square = 6 by 6
d) 64 inch square = 8 by 8
Factors of 66 = 2 x 3 x 11
Factors of 72 = 2 x 2 x 2 x 3 x 3
Now, we can see that in both 66 and 72 , we have 2 x 3 common that is 6.
And square of 6 is 36.
So, the answer is option C.