Constant of proportionality is given by: y=kx oy
![k=(y)/(x)](https://img.qammunity.org/2019/formulas/mathematics/college/yvbsu5pnyw56xx15nl1m8l8r1w2b23np4q.png)
So lets suppose y = 50 and x = 5 so k will be
![(50)/(5)=10](https://img.qammunity.org/2019/formulas/mathematics/middle-school/mmsmagvhn9y25vwysyhz6u5z6jdehz50sw.png)
This 10 will remain constant. For every $50 Michael saves $5, for $100 he will save $10 , for $150 he will save $15 and so on.
So this 'k' will be same for each value of x and y.