Or….try this 30 + min workout:

Warmup Level
3 min on level 4,6,8,6,4

1 min L1 sprint
2 min on level 4,6,8,6,4

1 min L1 sprint
1 min on level 4,6,8,6,4

Cool down

*Extra challenge : every minute is broken into 30 sec moderate/30 second faster (speed kept between 6-10 if possible) Every elliptical is different so your levels may have to be modified accordingly so that every 30 second hard interval is very hard.
Let me know how you do !