№674 2 приклад (99-9y)*8+14=86

(99-9у)*8+14=86
(99-9у)*8=86-14
(99-9у)*8=72
99-9у=72:8
99-9у=9
-9у=9-99
-9у=-90
у=-90:(-9)
у=10

(99-9*10)*8+14=86
(99-90)*8+14=86
9*8+14=86
72+14=86
86=86