The solution equation: X / 2 + X / 6 + X / 12 + X / 20 + X / 30 = 5 I can't do it now

The solution equation: X / 2 + X / 6 + X / 12 + X / 20 + X / 30 = 5 I can't do it now

You're lazy,
Tongfen: 50x = 300
x=6

20% = 12% * (x + 800) how to solve the equation
What's wrong with 20% x = 12% * (x + 800)

20%X=12%*(X+800)
X+800=20%X/12%
X+800=5X/3
3X+2400=5X
2X=2400
X=1200

10x (80 = 70) - 500, solve the equation, note that x is the letter

What's wrong with the title?
If it is: 10x (80-70) = 500
100x=500
x=5
If it is: 10x (80 + 70) = 500
1500x=500
x=1/3
If it is: 10x (80 + 70) - 500 = 0
1500x=500
x=1/3