Let's call the number you thought of n. Then what the two steps you took can be written as an equation:
[tex]n+4\frac{5}{7}=12n[/tex]
Subtract n to get all of your variables to one side:
[tex]4\frac{5}{7}=11n[/tex]
At this point, I recommend turning your mixed number into an improper fraction. It will make things easier later on:
[tex]\frac{33}{7}=11n[/tex]
Now divide both sides by 11 to get the value of n:
[tex]\frac{3}{7}=n[/tex]
