Bonjour,
1/3÷(4/9+1/7)
= 1/3 : (4 x 7 / 9 x 7 + 1 x 9 / 7 x 9)
= 1/3 : (28/63 + 9/63)
= 1/3 : 37/63
1/3 x 63/37
= 63/111
= 3 x 21 / 3 x 37
= 21/37
-7/10-(4/9+11/9)
= - 7/10 - 15/9
= - 7 x 9 / 10 x 9 - 15 x 10 / 9 x 10
= - 63/90 - 150/90
= - 213/90
= 3 x - 71 / 3 x 30
= - 71/30
(5/8-3/4)×11/15
= (5/8 - 3 x 2 / 4 x 2) x 11/15
= (5/58 - 6/8) x 11/15
= - 1/8 x 11/15
= - 11/120