Hello, thank you for taking the time to post your question!
The general form that you want to operate under here is slope-intercept form, meaning y = mx + b. since the lines are parallel you can just pull the slope out of the other equation directly … m = -1/2
From there then we can use the equation to solve for the y-intercept for the new line
y = -1/2x + b
2 = -1/2(4) + b
2 = -2 + b
4 = b
Putting it all together then the final equation for the new line is y = -1/2x + 4
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)