Place Value Problem: Find the Number 3-5-7 in Expanded Form

To solve this problem, we will construct the number using the given digits:

• Step 1: Calculate the contribution of the hundreds digit.
  The hundreds digit is 3, so it contributes $3 \times 100 = 300$.
• Step 2: Calculate the contribution of the tens digit.
  The tens digit is 5, so it contributes $5 \times 10 = 50$.
• Step 3: Calculate the contribution of the units digit.
  The units digit is 7, so it contributes $7 \times 1 = 7$.
• Step 4: Sum up all these contributions to get the final number.
  Therefore, the number is $300 + 50 + 7 = 357$.

Thus, the number that satisfies the given conditions is $\mathbf{357}$.