Найди корень уравнения -0,1f+10=9 f= ?

-0,1f + 10=9                                                                                                        
-0,1f = 9-10
-0,1f =-1    | * (-1)
0,1f = 1
f = 1 / 0,1
f = 10

-0,1f+10=9
-0,1f=9-10
-0,1f=-1
f=10
ответ: f=10