Answer:
B : 9 x 10
Explanation:
So i am just going with what i think it is going on here...
4 x 10 5 : 4 x 10 x 10 x 10 x 10 x 10 = 400000 (not a perfect square)
9 x 10 4 : 9 x 10 x 10 x 10 x 10 = 90000 (a perfect square)
4 x 10 3 : 4 x 10 x 10 x 10 = 4000 (not a perfect square)
9 x 10 3 : 9 x 10 x 10 x 10 = 9000 (not a perfect square)
(sorry if i'm wrong but i hope this helped)
my i add this took me so long to multiply and stuff