With a head start of 10 miles, Ted's line starts at 10 when time is zero, or the point (0,10).  For every hour that passes, Ted's distance increases by 10 miles.  This rate of change is the slope of his line ( m = 10).
Ted's equation:  y = 10x + 10

Jason's line starts at zero since he did not get a head start, or at the point (0,0).  For every hour that passes, Jason's distance increases by 20 miles.  This rate of change is the slope of his line ( m = 20).
Jason's equation:  y = 20x + 0

Jason will catch up with Ted when the two lines intersect or after one hour.

They will have traveled 20 miles when they meet.