[(720:8- n)·7+395]·2=1 700
[( 90- n)·7+395] =1 700:2
( 90- n)·7+395 = 850
( 90- n)·7 = 850-395
(90- n)·7 = 455
( 90- n) = 455:7
90- n = 65
n = 90-65
n = 25
[(720:8- 25)·7+395]·2=1 700
[( 90- 25)·7+395]·2 =1 700
(65·7+395)·2 =1 700
( 455+395 )·2 =1 700
850·2 =1 700
1 700=1 700
