What is the constant of proportionality of a graph if x equals 3 and y equals 90?

y = kx

'k' is the constant of proportionality, or otherwise known as constant of variation.

y = 90

x = 3

90 = k (3)

90 = 3k

3k/3 = 90/3

k = 30

The constant of proportionality is 30.