bonsoir
a) ( 7/4 - 5/6) x 8/3 = ( 21/12 - 10/12 )x 8/3 = 11 /12 x 8/3 = 88/36 = 22/9
b) - 7/8 : ( - 1/5 - 9/10 ) = - 7/8 : ( - 2/10 - 9/10) = - 7/8 : - 11/10 = - 7/8 * - 10/11
= 70/88 = 35/44
c) ( 4/15 - 3/10 ) : ( - 11/6 + 7/4 ) = ( 8/30 - 9/30) : ( - 22/12 + 21/12)
= - 1/30 : - 1/12 = - 1/30 x - 12 = 12/30 = 2/5