(83a-91b)-(89a-100b)
(5k+6t)+(2.8t-3.1k) 
решите пж прошу вас

 1)

   (83a-91b)-(89a-100b) =

=  83a-91b - 89a+100b =

=  (83a-89a)+(100b-91b) =

= - 6a + 9b = - 3(2a - 3b)

2)

   (5k+6t)+(2.8t-3.1k) =

= 5k+6t + 2,8t - 3,1k =

= (5k-3,1k)+(6t+2,8t) =

= 1,9k + 8,8t