Bonsoir
a. - 28/35 = (7 x - 4) / (7 x 5) = - 4/5
b. 40/48 = (8 x 5) / (8 x 6) = 5/6
c. - 63/- 49 = (7 x 9) / (7 x 7) = 9/7.
