We can start by the simplest factor. Which is 2.
24:18 will be divided by 2 both sides.That will be 12:9.
We then realize that 12 and 9 are both multiples of 3.
So we take 12:9 divided by 3 on both sides again.Which would be 4:3.
The factors end here which will give us 4:3 as the simplest form.
Hope this helps !!