Equation says this:

But the book tells me it can also be written like this:

I got confused on how that could be so I tried to get the second expression of a line from the first expression of the line by trying cross multyplication:

But I get this which is close but not it:

Although when I do this:

I get something that resembles the equation in the second part:

Am I doing something wrong here? How does this form a line exactly because I grew up with the y = mx+b equation and this is the first time I am seeing this.