A line has a slope of 2 and passes through the midpoint of the segment connecting (2,3) and (6,9). What is the y-intercept of the line?

First find the midpoint by averaging coordinates: $\left(\frac{2+6}{2}, \frac{3+9}{2}\right) = (4, 6)$. The line has slope 2, so $y = 2x + b$. Substitute the midpoint: $6 = 2(4) + b$, so $b = -2$, choice C. Check: at $x = 4$, $y = 8 - 2 = 6$. Choice A (6) is the midpoint's $y$-coordinate, which is not the intercept since the line does not pass through $x = 0$ there. Choice B (4) is the midpoint's $x$-coordinate. Choice D (2) comes from sign error: $6 - 8 = -2$, not $+2$.