aider moi je ne comprend pas du tout

bonsoir

a) 4/5 + ( 7/3 x 6) = 4/5 + 42/3 = 12/15 + 210/15 = 222/15 =  = 74/5

b) ( 5 + 9) x ( 3 : 8)
b = 14 x 3/8 = 42/8 = 21/4

c) (10/9 + 5/18) x ( 6 - 3/5)
c = ( 20/18 + 5/18) x ( 30/5 - 3/5)
c = 25/18 x 27/5 =  675/ 90 = 15/2

d = ( 4/7 x 21/5) + (2/15 x 6/7)
d = 84/35  + 12/105
d = 252/105 + 12/105 = 264/105= 88 / 35