Answer: A

The slope is $\frac{10 - 7}{9 - 3} = \frac{1}{2}$. Using $(3, 7)$: $7 = \frac{1}{2}(3) + b$, so $b = \frac{11}{2}$ and $y = \frac{1}{2}x + \frac{11}{2}$. At the $x$-intercept $y = 0$, so $\frac{1}{2}x = -\frac{11}{2}$ and $x = -11$.

Choice C uses the $y$-intercept value, $\frac{11}{2}$, as the $x$-coordinate of the $x$-intercept.

Why the other choices are wrong

• B. This is the opposite of the y-intercept. To get x, divide -11/2 by the slope, 1/2.
• C. 11/2 is the y-intercept of the line, where x = 0, not the x-intercept.
• D. This makes a sign error. Setting y = 0 gives (1/2)x = -11/2, so x is negative.