Question

Selena babysits on the weekends. The equation y = 12x represents the amount of money she earns for every hour, x, she babysits. What is the constant of proportionality?

Answer 1

The answer to your question is twelve.

Answer 2

The constant of proportionality is the ratio of y to x.

To find the constant of proportionality of y = kx we divide out x. Note, k = constant of proportionality.
y = kx
y / x = kx / x
y / x = k
k = y / x
Notice y / x is our ratio of y to x. Now knowing this we can see that 12 is in the k spot of y = 12x and 12 is our constant of proportionality.