Question

16 is 25% of what number

Answer 1

So the question is 16 is 25% of what number (x)

In math
"is" means equals
"of" means times

The question translates to

16 = 25% * x
16 = .25x
16/.25 = x
64 = x

x = 64

16 is 25% of 64

Answer 2

25% of 16 can be written as:

25% × n  = 16 (Where n represents the number which 16 will be 25% of)

25% × n is the same thing as saying:

1/4 × X = 16
X/4 = 16
X/4 × 4 = 16 × 4
X = 64

This may be a bit confusing, if you require clarification, let me know!