bonjour
M = - 14 /15 + 10 /15 : 20/7
M = - 14/15 + 10 /15 * 7 /20
M = - 14 /15 + 70 / 300
M = - 280 /300 + 70 / 300
M = - 210 /300
M = - 7 / 10
N = 3/15 - 42/ 5 * ( - 15 /42 + 10 /42 )
N = 3 /15 - 42 / 5 * - 5 /42
N = 3/15 + 210 / 210
N = 3/15 + 1
N = 3/15 + 15/15
N = 18 /15 = 6 /5