Let "x" represent the number of hours Elisha works, if she gets paid $13 per hour, the amount she earns after working "x" hours can be expressed as $13x.
So the function that expresses he earnings is
[tex]f(x)=13x[/tex]
Now, this is true only for values of x greater than or equal to 0, since it makes no sense for someone to work "negative hours" the variable x should not take negative values.
The restriction for the domain can be expressed as follows:
[tex]\mleft\lbrace x|x\ge0\mright\rbrace[/tex]
