The constant of proportionality is 6. This means that for every 1 quart increase in blue paint, there is a 6 quart increase in red paint.
The graph shows a proportional relationship between the number of quarts of blue paint in the mix and the number of quarts of red paint. The constant of proportionality is the slope of the line, which is equal to the change in y divided by the change in x.
In this case, the line passes through the points (2, 12) and (3, 18). The change in y is 18 - 12 = 6, and the change in x is 3 - 2 = 1. Therefore, the slope of the line is 6/1 = 6.
So the constant of proportionality is 6. This means that for every 1 quart increase in blue paint, there is a 6 quart increase in red paint.
Therefore the constant of proportionality is 6.