1 and 3/8 is equivalent to 11/8 which is one lap. If she ran 3 laps, you would multiply 11/8 by 3 which would get you 33/8- which is equivalent to 4 and 1/8.
Substitution is plugging one equation into the other. Elimination is where you eliminate one equation. Graphing is when you graph the equations and see where they overlap.