Final answer:
The y-intercept for the regression line y = 21 - 5x is 21, which is where the line crosses the y-axis when x is zero.
Step-by-step explanation:
For the regression line y = 21 − 5x, 21 is indeed the y-intercept of the line. The equation of a line in slope-intercept form is y = mx + b, where m is the slope and b is the y-intercept. The y-intercept is defined as the value of y when the independent variable x is zero.
Applying this to the equation y = 21 − 5x, the slope is -5, and the y-intercept is 21. This means that the line crosses the y-axis at the point (0, 21). Therefore, when responding to whether 21 is the y-intercept for the equation provided, the answer is yes.