SVP pour demin ex 5 et 7 j'y arrive pas

Ex 5 : 

a) 3x
b) xy
c) 12
d) 7b
e) 7ab
f) 3a+ 24

Ex 7 :

a) 8 x 3 = 3 = 24 + 3 = 27
b) 24 - 7 x 3 = 24 - 21 = 3
c) 5 x (3 + 8) = 5 x 11 = 55
d) 3 x (14 - 2 x 3) = 3 x (14 - 6) = 3 x 8 = 24
e) 3² = 3 x 3 = 9
f) 3³ = 3 x 3 x 3 = 9 x 3 = 27