(6b-9)(9b+6)-9b(6b+9) при b=5,3

(6b-9)(9b+6)-9b(6b+9)= 54b²-81b+36b-54-54b²-81b= -81b+36b-54-81b= -126b-54= -126×5,3-54= -667,8-54= -721,8