How many ways can a rectangular box equal to 100 meter square?

Answer 1

An infinite number of ways.

Pick any number greater than or equal to 10 - there are an infinite such numbers. Call that number L (for length)

Calculate B = 100/L.

then it is easy to show that every different L gives a B that is different from other Bs and from any Ls

and

L*B = L*100/L = 100

So each value of L gives a different solution.

Since there are in infinite number of Ls, there are an infinite number of ways.