What integer is the opposite of positive 7

Find the value of 1715⋅211.though these numbers aren't quite as nice as the ones from the example or the previous part, the procedure is the same, so this is really no more difficult. give the numerator followed by the denominator, separated by a comma.

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9