The cube has all sides the same length (even if the diagram may not look like it). The volume is V = length*width*height = 5*5*5 = 125 cubic cm. The answer is choice A.
The number is 20,607. The "20 thousand" portion can be written into 20*1000. Effectively, we have 20 copies of "1000" being added, so we can shorthand that into multiplication. The same idea applies to 6*100 which represents 600. Overall we can say 20,607 = 20*1000+6*100+7. The answer is choice C.