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When the signs are similar 
We will add the number
Bring down the common sign of the number

When the signs are different
We will subtract their absolute value
Bring down the number with greater absolue value

Please don't delete nor copy my answer...
This is based on my mind

≡ω∈ω⇒In his second book of poetry and winner of the 2000 T. S. Eliot Prize, H. L. Hix uses two contrasting poetic sequences. "Orders of Magnitude" defies rationality in favor of invention in the musical sense: producing a short composition that works out a single idea. As in music, the whole composition achieves its irrational effect through rational formal structure, with 100 poems, each ten lines long, with ten syllables per line. In the second sequence, "Figures," the speakers follow their "pure" rationality, though it leads them--inevitably--into the dark heart of the irrational. The result is a ledger of love and loss, a balancing of grief's books. Every reader will recognize the accounting in Rational Numbers.