x is one of the numbers
Since one number is 5 times the other, so it is 5x
And it is the sum, so the sign between 5x and x is plus
The equation of this question is 5x+x=12
5x and x are like terms, so you combine them and get 6x.
Now the equation became 6x=12
So you divide 6 to both side and get x=2