①6x+31=49,
6x+31-31=49-31,
6x=18,
6x÷6=18÷6,
x=3;
②7x÷3=8.19,
7x÷3×3=8.19×3,
7x=24.57,
7x÷7=24.57÷7,
x=3.51;
③32.8-9x=17.5,
32.8-9x+9x=17.5+9x,
17.5+9x=32.8,
17.5+9x-17.5=32.8-17.5,
9x=15.3,
9x÷9=15.3÷9,
x=1.7;
④x-0.36x=16,
(1-0.36)x=16,
0.64x=16,
0.64x÷0.64=16÷0.64,
x=25;
⑤6×7+3x=69,
42+3x=69,
42+3x-42=69-42,
3x=27,
3x÷3=27÷3,
x=9;
⑥6x+2x-56=0,
(6+2)x-56+56=0+56,
8x=56,
8x÷8=56÷8,
x=7.