Je ne comprends pas qui veut bien me donner la rep avant jeudi

bonjour
exercice 1
a. 240 = 2⁴ x 3 x 5
b. 312 = 2³ x 3 x 13
b ) PGCD = 2³ x 3 = 24
c) 312/240 = 13/ 10
exercice 3
A = 2/7 - 3/7 x 14 /9
= 2/7 - 42/63
= 18/63 - 42/63
= - 24/63
= - 8/21
B = - 7/8 x ( 2/3 - 1 )
= - 7/8 x ( 2/3 - 3/3)
= - 7/8 x - 1/3
= 7/24
D = - 2/5 : 3/15 + 2/15
= - 2/5 x 15/3 + 2/15
= - 30/15 + 2/15
= - 28/15
C = 4/5 x 1/4 + 2/5
= 4/20 + 8/20
= 12/20
= 3/5
E = 9/2 - 5/2 : 15/8
= 9/2 - 5/2 x 8/15
= 9/2 - 40/30
= 9/2 - 4/3
= 27/6 - 8/6
= 19/6