Hello!
The answer is:
If the red line has a slope of 3, the slope of the red line will also be 3.
So, the correct option is, D. 3
Why?
We need to remember that if two or more lines are parallel, they will share the same slope, no matter where are located their x-intercepts and y-intercepts, the only condition needed for them to be parallel, is to have the same slope.
So, if two lines are parallel, and one of them (the red line) has a slope of 3, the slope of the other line (the green line) will also be 3.
Have a nice day!