Each hour she works, she earns [tex]x[/tex] dollars.
The first day, she worked 6 hours, so she'd earn [tex]6x[/tex] dollars.
The second day, she worked 8, so she'd earn [tex]8x[/tex].
Together, she'd have earned [tex]6x+8x[/tex] dollars.
You could add the number of hours she worked first and then multiply by [tex]x[/tex] to get the same result. This would look like [tex](6+8)x[/tex].