Step-by-step explanation:
If we have two variables and can write a relationship between them as:
![y=kx \\ \\ \\ Where: \\ \\ \text{k is the constant of proportionality}](https://img.qammunity.org/2021/formulas/mathematics/middle-school/kzx8yecftvx53y0geo4nx3btqysjrxom45.png)
Then we say that
varies directly as
or
is directly proportional to
![x](https://img.qammunity.org/2021/formulas/mathematics/middle-school/p9sq9b3rc5nwoqzhzc8wcaj51b36281l9g.png)
In this case, let's say:
![x:\text{The number of hours worked} \\ \\ y:\text{Total work fee}](https://img.qammunity.org/2021/formulas/mathematics/middle-school/anghe6jh805l76g7soq5t3sbbkengwd36t.png)
Then since we know that the fee for 5 hours of work is $255, then the constant of proportionality is:
![k=(255)/(5) \\ \\ k=51](https://img.qammunity.org/2021/formulas/mathematics/middle-school/l4sln51jc0sntflep8gshlzb7eoxzbbcep.png)
Therefore, our model can be written as:
![\boxed{y=51x}](https://img.qammunity.org/2021/formulas/mathematics/middle-school/1q4hdyh4q6l2cq3emd4tm3oicbk5ikrv02.png)