Let's break down the expression step by step:

1. Calculate \( 25 \times 4 \):
\[
25 \times 4 = 100
\]

2. Calculate \( 8 \times 125 \):
\[
8 \times 125 = 1000
\]

3. Add the results of the two multiplications:
\[
100 + 1000 = 1100
\]

4. Now, we need to interpret the part after the underscore. It looks like it might be a division operation, but the format is unclear. Assuming it is division:
\[
3366 \div 33 = 102
\]

So, the expression \( 25 \times 4 + 8 \times 125 \_ 3366 \div 33 \) simplifies to:
\[
1100 \_ 102
\]

If the underscore represents concatenation, the final result would be:
\[
1100 \_ 102 = 1100102
\]

If it represents subtraction, the final result would be:
\[
1100 - 102 = 998
\]

Without further clarification, it's difficult to determine the exact intended operation for the underscore.