What is the least possible number of planks of timber 42 m, 49 m and 63 m long have to be divided into planks of the same length?

Step 1: Find the least common multiple (LCM) of the tolling intervals. The bells toll after 7, 8, 11, and 12 seconds. First, find the prime factorization of each number: $7 = 7^1$ $8 = 2^3$ $11 = 11^1$ $12 = 2^2 \times 3^1$

The LCM is the product of the highest powers of all prime factors present: $LCM(7, 8, 11, 12) = 2^3 \times 3^1 \times 7^1 \times 11^1$ $LCM = 8 \times 3 \times 7 \times 11$ $LCM = 24 \times 77$ $LCM = 1848 \text{ seconds}$ This means the bells will toll together every 1848 seconds.

Step 2: Convert the given time duration into seconds. The question asks about the next 3 hours. 1 hour = 60 minutes 1 minute = 60 seconds 1 hour = $60 \times 60 = 3600$ seconds 3 hours = $3 \times 3600 = 10800$ seconds

Step 3: Calculate how many times the bells will toll together again in the next 3 hours. The bells toll together at 9:00 a.m. We need to find how many times they toll together after this initial time within the 3-hour period. Divide the total time in seconds by the LCM: $\text{Number of times} = \frac{Total time}{LCM}$ $\text{Number of times} = \frac{10800}{1848}$ $\text{Number of times} \approx 5.844$ Since we are looking for the number of complete tolling cycles within the 3 hours, we take the floor of this value. The bells will toll together 5 more times within the next 3 hours.

The final answer is $\boxed{5}$.