To solve these equations, we'll go through each one step by step:

1) x : 13 - 18 = 23
First, we simplify the left side of the equation:
x - 5 = 23
Then, we isolate x by adding 5 to both sides:
x = 28

2) 1428 : x + 123 = 137
First, we simplify the left side of the equation:
1428 = 137(x + 123)
Then, we distribute 137 to both terms inside the parentheses:
1428 = 137x + 16851
Next, we isolate x by subtracting 16851 from both sides:
-15423 = 137x
Finally, we solve for x by dividing both sides by 137:
x = -113

3) 7 * x - 8 = 713
First, we simplify the left side of the equation:
7x - 8 = 713
Then, we isolate x by adding 8 to both sides:
7x = 721
Finally, we solve for x by dividing both sides by 7:
x = 103

4) (x - 1945) * 5 = 50
First, we simplify the left side of the equation:
5(x - 1945) = 50
Then, we distribute 5 to both terms inside the parentheses:
5x - 9725 = 50
Next, we isolate x by adding 9725 to both sides:
5x = 9775
Finally, we solve for x by dividing both sides by 5:
x = 1955

5) 246 - 3 * (x + 2) = 120
First, we simplify the expression inside the parentheses:
246 - 3x - 6 = 120
Next, we combine like terms:
240 - 3x = 120
Then, we isolate x by subtracting 240 from both sides:
-3x = -120
Finally, we solve for x by dividing both sides by -3:
x = 40

6) x : 125 = 75 ( dư 5)
This equation is a bit different because it includes a remainder. To solve it, we'll set up an equation using the given information:
x = 75 * 125 + 5
First, we multiply 75 by 125:
x = 9375 + 5
Then, we add 5 to 9375:
x = 9380

So the solutions to the equations are:
x = 28, -113, 103, 1955, 40, and 9380.