How do u determine which line is faster when comparing two lines on a time vs position graph? ?

Well, as we've discussed under another one of your questions, lines on graphs
don't have speed.  But the lines have slopes, and the slope of the graph at every
point is the speed of the object the line represents, at that time.

So if there are two lines on a position/time graph, the line with the steeper slope
represents a greater speed than the flatter line does.

Funny thing:  One line could even be dropping while the other one is rising.
That's OK.  It just means the objects are moving in opposite directions. 
The steeper line still indicates the faster speed.