bonjour svp ex 64 et 67

64)
a) 2/3 (- 7/5) - 9/10
= - 6/15 - 9/10
= - 6 x 2 / 15 x 2 - 9 x 3 / 10 x 3
= - 12/30 - 27/30
= - 39/30
= 3 x - 13 / 3 x 10
= - 13/10

b) 7/15 - 1/15 x 10/7
= 7/15 - 10/105
= 7 x 7 / 15 x 7 - 10/105
=  49/15 - 10/105
= 39/105
= 3 x 13 / 3 x 35
= 13/35

67) ?