Answer:
A proportional relationship is a relation of the form:
Y = A*X
This means that if we have two variables, X and Y, for each unit that X grows, Y grows A times that.
And notice that the relation:
Y/A = X
is also a porportional relationship
This relationship can be expresed in a graph as a straight line that pases through the origin and has a constant unit of growht (in this case A) that is also called the "slope" of the line.