What exactly are you trying to do? And also if there was a getSpeed() method (which unless I'm missing something, there isn't), your code should be written more like Greenfoot.setSpeed(Greenfoot.getSpeed() + 10)
You could add an 'public int runSpeed;' to the world class and in the world constructor, set the value and set the scenario speed at that time. Then when you need the value, you have it right there.
You could add an 'public int runSpeed;' to the world class and in the world constructor, set the value and set the scenario speed at that time. Then when you need the value, you have it right there.
It may also be an idea to make it static for easier access from other classes - I say easier in that you have to do:
YourWorld.runSpeed rather than (and this is only if the class extends Actor) ((YourWorld)getWorld()).runSpeed