How can you determine if a stretch or compression occurred, by looking at a graph of two linear functions?

If a linear function f(x) is transformed (shifted,compresses, stretched) than the graph of the function is changed.
Stretch or a compression is a non-rigid transformation of the function. Rigid transformation keep the same size and shape of the original function, and non-rigid transformation have changed size and shape.
A vertical stretching is the stretching of the graph away from the x-axis. A vertical compression is the squeezing of the graph towards the x-axis. A compression is a stretch by a factor less than 1. Horizontal stretching is the sameonly on the y-axis.