rephrase it:
-10r-r
= -11r when you subtract a negative from a negative, it is like adding, then you put the negative sign at the end.
It's actually an expression to be honest.
Nothing will be left of the galaxy, once one planet's orbit is thrown off, others will go off track or collide too.
1/6x100
=16.66666666666667
approx.= 17%