Answer:
The relationship between the circumference of a circle and its diameter represent a direct variation and the constant of proportionality is equal to the constant 
Step-by-step explanation:
we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form 
where K is the constant of proportionality
In this problem we know that
The circumference of a circle is equal to

therefore
the relationship between the circumference of a circle and its diameter is a direct variation and the constant of proportionality is equal to the constant 
It's 96 if you were wondering
12.6 million = 4p + 1 million
to solve:
12.6 million - 1 million = 4p + 1 million - 1 million
11.6 million/4 = 4p/4
2.9 million = p
the population in 1950 was approximately 2.6 million
Multiply both sides by 7.
-5 * 7 = c/7 * 7
-5 * 7 = c
c = -35
Your final answer is c = -35.