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!