The number m and 5/8 are additive inverses.
2 answers:
Conveniently, your number line has 8 divisions in each unit interval, so finding 5/8 is a matter of counting 5 divisions.
The additive inverse of a number has the opposite sign from the number, so m = -5/8. The sum of a number and its additive inverse is zero. (That is the definition of additive inverse.)
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