Hello there!
The question seems to be incomplete, but going off what I assume you meant: If f(x) is parallel to the line y= 3/4x+2/5, the slope of the line would be the same as the slope in y = 3/4x + 2/5, or 3/4.
This is because lines are parallel when they have the same slope. :)
I hope this helps and have a great day! If this wasn't the question let me know and I can help you more in the comments ! :)