Bonjour

a. 3/17 - - 7/51

= (3 x 3) / (17 x 3) + 7/51

= 9/51 + 7/51

= 60/51

= (3 x 20) / (3 x 17)

= 20/17

b. - 11/20 - 7/- 100

= (- 11 x 5) / (20 x 5) + 7/100

= - 55/100 + 7/100

= - 48/100

= (4 x - 12) / (4 x 25)

= - 12/25

c. - 3 - 7/12

= (- 3 x 12) / (1 x 12) - 7/12

= - 36/12 - 7/12

= - 42/12

= (6 x - 7) / (6 x 2)

= - 7/2.