bonjour
A = 1/3 + ( 8/3 - 21/49 x 22/2) : 4/7
= 1/3 + ( 8/3 - 462/98) : 4/7
= 1/3 + ( 8/3 - 33/7) : 4/7
= 1/3 + ( 56/21 - 99/21) : 4/7
= 1/3 + ( - 43/21 : 4/7)
= 1/3 + ( - 43/21 x 7/4)
= 1/3 + ( - 301/84)
= 1/3 - 43/12
= 4/12 - 43/12 = - 39/12 = - 13/ 4