`7/12 + (-5)/9`
`= 63/108 + (-60)/108`
`=123/108`
__
`3/7 - 5/(-6) + 3/(-7)`
`= 3/7 - (-5)/6 + (-3)/7`
`= 3/7 + 5/6 + (-3)/7`
`= (3/7 + (-3)/7) + 5/6`
`= 0+5/6`
`=5/6`
`a)7/12+(-5/9)`
`=21/36+(-20/36)`
`=1/36`
__
`b)3/7-5/(-6)+3/(-7)`
`=3/7+5/6+(-3)/7`
`=3/7+5/6-3/7`
`=(3/7-3/7)+5/6`
`=0+5/6`
`=5/6`
a) 7/12+-5/9= 21/36+ -20/36= 1/36
b) 3/7- 5/-6 + 3/-7 = 3/7 - 3/-7 + 5/-6= 0 + 5/-6= 5/-6
\(a)\dfrac{7}{12}+\dfrac{-5}{9}\\ =\dfrac{7}{12}-\dfrac{5}{9}\\ =\dfrac{7.3}{12.3}-\dfrac{5.4}{9.4}\\ =\dfrac{21}{36}-\dfrac{20}{36}\\ =\dfrac{1}{36}\\ b)\dfrac{3}{7}-\dfrac{5}{-6}+\dfrac{3}{-7}\\ =\dfrac{3}{7}+\dfrac{5}{6}-\dfrac{3}{7}\\ =\left(\dfrac{3}{7}+-\dfrac{3}{7}\right)+\dfrac{5}{6}\\ =0+\dfrac{5}{6}\\ =\dfrac{5}{6}.\)