You haven't shared the given line, so all I can do here is to invent a line and then show you how to write the equation of a new line which is parallel to mine and which has an x-intercept of 4.
My invented line: y = (2/3)x + 3
The new line MUST have the same slope: m = 2/3.
Then y = mx + b becomes y = (2/3)x + b. Find the x-intercept by setting y = 0 and solving for x: (2/3)x = 0 - b. Now replace x with 4 and find b:
-b = (2/3)(4) = 8/3. Then b = -8/3, and the new line is
y = (2/3)x - 8/3.