We will investigate how to determine the constant of proportionality for specific relationship between two variables.
We are given the respect proportionality between two variables ( x and y ) on a cartesian coordinate plane as such:

We are to determine the constant of proportionality ( k ) for the relationship expressed between the two variables.
A general proportional relation between ( x ) and ( y ) is expressed as follows:

Where,

We will use the given data point ( x , y ) and the general expression for direct proportions to determine the value of the constant of proportionality ( k ) as follows:

We plugged in the respective quantities of the variables ( x ) and ( y ) and evaluated for the constant of proportionality ( k ):
