Need to get an idea of how to do these questions for finals could you possibly answer it so I can get a better understanding of the question

Answer:
[tex]y\text{ = 3x-21}[/tex]Explanation:
Here, we want to get the equation of the line
Mathematically, we have the equation of a straight line as:
[tex]y\text{ =mx + b}[/tex]where m is the slope and b is the y-intercept
From what we are given , the slope is 3
To the x-intercept, it is the value of x when y = 0. We can use this to get b
Mathematically, we have that as:
[tex]\begin{gathered} 0\text{ = 3(7) + b} \\ 0\text{ = 21 + b} \\ b\text{ = -21} \end{gathered}[/tex]The equation of the line is:
[tex]y\text{ = 3x-21}[/tex]