A line parallel to x-2y=6 has which slope? Solving for y, -2y = 6 - x, and
m = -1 / -2, or 1/2.
Then the slope-intercept formula, y = mx + b, becomes 4 = (1/2)(2) + b, and b is 3. Thus, the equation of this line is y = (1/2)x + 3.
Check: does the point (2,4) satisfy this equation? Is 4 = (1/2)(2) + 3 true? YES.
