In this situation, we would use something called the vertical line test. In other words, if we can draw a vertical line that passes more than one point on the graph, then the relation is not a function.
If we use the vertical line test in this situation, it is not possible to draw a vertical line that passes through more than one point. Therefore, this does represent a function.
You could use a simple pencil test to figure it out. Place a pencil vertically on the paper, and move it left to right or vise-versa When moving it make sure the pencil doesn't hit two points at once if it does it is not a function, but this is not the case
Segment ST is half and RS is the other half. RT is the whole line so adding ST and RS will get you RT. 4x-7+3x-8=4x. solve for x which will get you 5. Replace the x with 5 in 4x (for segment RT) will get you an answer of 20 for the whole line.
