Question 708719
Maybe we are in an alternate place where "add" and "take away" have the meaning familiar to me, but the symbols for numbers have different meanings.
9 is the number that added to other numbers does not change them, like our zero, and we call it the neutral number for addition.
6-9=6 <--> 6=6+9
6 and 10 are opposite numbers that add up to the neutral number for addition.
9-10=6 <--> 9=6+10
I have no idea what 40 and 50 mean, but I know that
40-50=6 <--> 40=6+50 <--> 40-6=50
and since 6 and 10 are opposites, taking away 6 means adding 10, so
{{{system(50=40-6,40-6=40+10)}}} --> 50=40+10,
which looks familiar, but it is just coincidence.