Bonjour!
D = (1/5 - 8/15) × 5/4
D = (1*3/5*3 - 8/15) × 5/4
D = (3/15 - 8/15) × 5/4
D = -5/15 × 5/4
D = -25/60
D = -5*5/5*12
D = -5/12
Voila! J'espere t'avoir aide! :)
