The x-intercept is the point where the line crosses the x-axis, i.e., when y = 0. Therefore, (-1, 0) is a point on line a.
Likewise, y = -1 when x = 0, so (0, -1) is also a point on line a.

Now that we have 2 points on line a, we can find its slope:
\(\frac{y2-y1}{x2-x1} = \frac{-1-0}{0-(-1)} = -1\)

Since lines a and b are parallel, they have the same slope. We can plug in the given point (10, 20) into the equation y = mx+b:
\(20 = (-1)(10) + b\)
\(b = 30\)