Algebra-1

Question Analysis
This question tests the student's ability to calculate the constant rate of change (slope) of a linear relationship using two given points. 

Key Concept Explanation
The constant rate of change, or slope, of a linear relationship is the ratio of the change in the dependent variable (y) to the change in the independent variable (x). It is calculated using the formula .

Step-by-step Solution
1. Identify the coordinates of the two points: (4, 9) and (6, 21).
2. Apply the formula for the constant rate of change:

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