Bonjour svp pouvez vous m’aider à mon exo de math à la C,D,E,F

Bonjour
C = 3/5 + 6/5
C = 9/5
D = 3/5 x 6/5
D = 18/25
E = 5/6 x 3/15
E = 15/90
E = (15 x 1) / (15 x 6)
E = 1/6
F = 3/20 - 5/4
F = 3/20 - (5 x 5) / (4 x 5)
F = 3/20 - 25/20
F = - 22/20
F = (2 x - 11) / (2 x 10)
F = - 11/10.