well this is kinda going to be self explantiory just subtract so like 7-8, turn the 7 into 17 and so do 17 -8 which is 9. And since you cannot do 7-8 you have to take the 1 from the 1.7 right so 1-0 will turn into 0-0 with is 0! so 0.9 will be your answer, hopethis helps!
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