Exercice 3 et 4 svp urgent :((

Ex 3 :

A = 4/21 + 5/3
A = 4/21 + 35/21
A = 39/21
A = 13/7

B = 4/9 - 7/15
B = 20/45 - 21/45
B = - 1/45

C = - 10/8 * - 24/15 * - 1/6
C= 240/120 * - 1/6
C = - 240/ 720
C = - 1/3
    
D = (- 12/25)/(- 9/15) ⇒ Diviser c'est multiplier par l'inverse.
D = - 12/25 * - 15/9
D = 180/225
D = 4/5

Ex 4 :

a) 9⁻¹⁵

b) -3⁻⁴

c) 7⁻⁸

d) 9¹¹