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

1) 12 + x + 24 + 14 = 921
Combine like terms: x + 50 = 921
Subtract 50 from both sides: x = 871

2) 724 + 15 - (18 + x) = 268
Combine like terms inside the parentheses: 724 + 15 - 18 - x = 268
Combine like terms: 721 - x = 268
Subtract 721 from both sides: -x = -453
Divide by -1 to solve for x: x = 453

3) 252 - (52 + x) + 78 = 178
Combine like terms inside the parentheses: 252 - 52 - x + 78 = 178
Combine like terms: 278 - x = 178
Subtract 278 from both sides: -x = -100
Divide by -1 to solve for x: x = 100

4) (x + 735) - (535 - 50) = 300
Combine like terms inside the parentheses: x + 735 - 535 + 50 = 300
Combine like terms: x + 250 = 300
Subtract 250 from both sides: x = 50

5) 36 ÷ 8 × 2 = 12
Perform the division: 4 × 2 = 12

6) (125 × x) ÷ (50 ÷ 2) = 40
Perform the division inside the parentheses: (125 × x) ÷ 25 = 40
Multiply both sides by 25: 125 × x = 1000
Divide by 125 to solve for x: x = 8

7) 75 ÷ (x × 5) × 4 = 20
Perform the division inside the parentheses: 75 ÷ (5x) × 4 = 20
Multiply both sides by (5x): 300 = 20 × (5x)
Divide by 20 to solve for (5x): 15 = 5x
Divide by 5 to solve for x: x = 3

8) 1200 ÷ 200 × x ÷ 9 = 2
Perform the division: 6 × x ÷ 9 = 2
Multiply both sides by 9: 6x = 18
Divide by 6 to solve for x: x = 3

9) 175 × x × 2 ÷ 350 = 8
Perform the multiplication: 350x ÷ 350 = 8
Divide by 350 to solve for x: x = 8/350