bonjour
A = 1/7 + 3/2 * 3/2 * -10/21
= 1/7 + 9/4 * -10/21
= 1/7 - 90/84
= 1/7 - 15/14
= 2/14 - 15/14 = - 13/14
B = 4/5 : ( - 3/7) - 7/10
= 4/5 * - 7/3 - 7/10
= - 28/15 - 7/10
= - 56/30 - 21/30
= - 77/30
C = 3/2 + 3/5 * 5/4 - 3/8
= 3/2 + 15/20 - 3/8
= 60/40 + 30/40 - 15/40
= 75/40 = 15/8