If "a < b" why is "3 - a > 3 - b"

okay so I have to make an argument for that, I know it's because there's the negative thing but I need to make it clearer/more detailed. thanks xx

When you multiply by -1 you change the direction of the " greater than sign"
eg 2 > -1 multiply by -1
- 2 is NO longer > 1, so it' becomes
-2 < 1

so a > b multiply by -1
- a < - b +3 both sides
3 - a > 3 - b

If you subtract 2 numbers from the same number, you take less off that number when subtracting the smaller number.
if a=1 and b=2
1<2
3-a=3-1=2
3-b=3-2=1
2>1 therefore 3-a>3-b