Ответ:

1) 27 : x + 405:9 = 48

2) 613x - 54x = 8385

559x = 8385; x = 15.

3) (27x -81): 3 = 18

4) (16x - 64): 7 = 64

5) 86 - (2x + 15) = 39

86 - 2x - 15 = 39; -2x = 39 - 86 + 15;

-2x = -32; x = (-32) : (-2); x = 16.

6) 2(3x + 70) = 350

6x + 140 = 350; 6x = 350 - 140; 6x = 210; x = 210 : 6; x = 35.

7) 6x + X-35 = 21

7x - 35 = 21; 7x = 21 + 35; 7x = 56; x = 56 : 7; x = 8.

8) 17y + 14y = 279

31y = 279; y = 279 : 31; y = 9.

9) 5y + 9y + 32

14y + 32; 2(7y + 16).

10) 200 + 28x + 35x = 504

200 + 63x = 504; 63x = 504 - 200; 63x = 304;

11) 203x - 184x = 608

19x = 608; x = 608 : 19; x = 32

12) 305x - 16.3 = 1782​

305x = 1782 + 16,3;

305x = 1798,3;