The answer is y=3x-2, but if you want to know how I found it, I wrote it out below :).
Okay, here's how I like to do these ones. It helps me if I actually graph these so I am going to attach some pictures of how I did this problem. To start off, just know that slope intercept form is y=mx+b, which is important in this problem and I will explain it more as we go on.
First, start off with drawing your x and y axes and then plot the points (2,4) and (5,13). Connect them using a ruler or something straight. It should look like the first picture I attached.
After that, count how many squares up the line is and how many over to make a right triangle, like I did in the second picture. After that, I like to think of rise over run, so you rise 9 vertically and run 3 horizontally. Make that into a fraction, and you should get 9/3. Divide that to get 3. This is your "m" value, or the slope.
Since we know that the slope is 3, that means that we can count on our graph to find the y intercept, or the "b" value. I did it out on the picture just to show you. The blue represents the rise, or 3 down and the green represents the 1 over, or the run. You are going to want to count down until you reach the y axis. The line meets the y axis at -2, so that means the the y intercept, or your "b" value is equal to -2.
If you put both values together, you should get the equation y=3x-2.
Hopefully that wasn't too confusing. Again, this is just how I like to do these, I don't know if there is a different way your teacher wants you to do it but I think it is easier to visually see what is happening.
Hope this helps!