Ok, let's back way up then.
The point is (9, -2) which means that at a particular point on the line, x=9, and y=-2.
The slope is 3/7 which means from any point on the line, you can go up 3 units then to the right 7 units and find another point on the line.
An equation of the line will be such that you can take the x and y coordinates from any point on the line and put them into the equation and make it a true statement.
The slope is found by dividing the difference between the y coordinates of two points by the difference between the x coordinates of those two points (rise-over-run).
Good, then the equation is true.
For triangle RST, do you know how to measure the sides using the distance formula (i.e. the pythagorean theorem)? As a hint, notice the symmetry and how the sides RS and RT look to be the same length.
The coordinates of points S and T are given. S is at (-4,7) and T is at (4,7). They are both at the height y=7, so it is a straight horizontal like going from x=-4 to x=4. How far is that?
There are particular skills and knowledge that these questions are testing from you. It is important that you have these basic skills proficiently so that you can move on to more difficult problems.