5x*7y*3b

To simplify the expression \( 5x \cdot 7y \cdot 3b \), you can multiply the coefficients (the numbers in front of the variables) together and write the variables together.

1. Multiply the coefficients: \( 5 \times 7 \times 3 = 105 \).
2. Combine the variables: \( x \cdot y \cdot b = xyz \).

So, the simplified expression is:

\[ 105xyz \]

If you'd like to see a different kind of operation or have further questions, let me know!