1. What is the constant of proportionality?
2. What is the equation?

Answer:
y = 1/3a
Step-by-step explanation:
y = ka
1 = 3k
k = 1/3
Confirm constant: (4-1)/(12-3) = 3/9 = 1/3
1 = 3(1/3) + b
1 = 1 + b
b = 0
y = 1/3x or 1/3a