Bonjour
a) 3/16 + 7/12
= (3 x 3) / (16 x 3) + (7 x 4) / (12 x 4)
= 9/48 + 28/48
= 37/48
b) 4/19 - 7/20
= (4 x 20) / (19 x 20) - (7 x 19) / (20 x 19)
= 80/380 - 133/3/80
= - 53/80
c) 3/10 + 11/4
= (3 x 2) / (10 x 2) + (11 x 5) / (4 x 5)
= 6/20 + 55/20
= 61/20.