Complete the math problem.

Solution:

1. Calculate the first part: \( 100 : 20 = 5 \).
2. Calculate the second part: \( 7 + 5 = 12 \).
3. Multiply the results: \( 5 \cdot 12 = 60 \).
4. Calculate the third part: \( 8 \cdot 3 = 24 \).
5. Calculate the fourth part: \( 40 - 24 = 16 \).
6. Subtract the fourth part from the third part: \( 60 - 16 = 44 \).
7. Subtract 31 from the result: \( 44 - 31 = 13 \).

Answer: 13