What is 15 of 250% percent of what number

Assuming the question is: '15 is 250% of what number'.

We can write an equation.

'is' indicates an equal sign

'of' indicates multiplication

'what number' indicates an unknown number we can call 'x'

So we have:

15 = 250% * x

or

15 = 2.5x

Divide 2.5 to both sides:

x = 6