An easy way to start a graph is by finding two points for the slope, and then a single point for the intercepts.
The two points I'll use are (0, 80) and (1, 120) (Keep in mind, you can use any two points, they'll all give you the rame ratio).
Use the slope equation:
![b = ((y_2-y_1))/((x_2-x_1)) \\b=((120-80))/((1-0)) \\b=(40)/(1) \\b=40](https://img.qammunity.org/2021/formulas/mathematics/high-school/g0hbtdfv5qwqp6621so1uos7ceuvbpb159.png)
Now that we have our slope, we can use one of the points (I'll just use (0, 80)) to create the equation.
![y-y_1=b(x-x_1)\\y-80=40(x-0)\\y-80=40x\\y=40x+80](https://img.qammunity.org/2021/formulas/mathematics/high-school/ncyubr7u098a6m28p9iebzn3cmvj05wnch.png)
So your final equation is y=40x+80.
* To solve for that second question, just plug in 10 for x and you should get the cost!