1. add the numbers → 25-4x = 15-3x+10-x
↓
25-4x = 25-3x-x
2. collect like terms 25-4x = 25-3x-x
↓
25-4x = 25-4x
3. the statement is true because if you subtract 25 from both side you are left with
-4x = -4x
then you would divide both sides by -4 to get
x=x which has infinitely many solutions and is rational/true