You solve a division problem with a three digit divisor in the same way you solve a division problem with a one or two digit divisor. The only difference is that the divisor is larger. Here's an example:
+------ 100 | 3455
1. Divide (or estimate) 2. Multiply 3. Subtract 4. Bring Down (and repeat) or Remainder
34 r55 1. Divide (345/100=3) +------ 2. Multiply (100 x 3 = 300) 100 | 3455 3. Subtract (345 - 300 = 45) 300 4. Bring down the 5 ------ 5. Divide (455/100=4) 455 6. Multiply (100 x 4 = 400) 400 7. Subtract (455 - 400 = 55) ----- 8. Remainder 55 55