If 15:1x::1x:11.25, then x=?

This is a proportion problem. We can solve it by cross-multiplication.

The given proportion is 15:1x::1x:11.25.

Cross-multiplication gives us:

15 * 1x = 1x * 11.25

This simplifies to:

15x = 11.25x

To solve for x, we subtract 11.25x from both sides:

15x - 11.25x = 0

This simplifies to:

3.75x = 0

Finally, we divide both sides by 3.75 to solve for x:

x = 0 / 3.75

So, x = 0.