The intervals for bells A, B, and C are 30, 35, and 40 minutes, respectively.

Find the prime factorization of each interval:

Interval of A (30 minutes): 2 * 3 * 5
Interval of B (35 minutes): 5 * 7
Interval of C (40 minutes): 2^3 * 5
Identify the highest power of each prime factor:

2^3, 3, 5, 7
Multiply the identified factors:
LCM(30, 35, 40) = 2^3 * 3 * 5 * 7 = 840 minutes

Now, the bells A, B, and C will ring together every 840 minutes.

Starting at 8:00 p.m., the next time they will ring together is at 8:00 p.m. + 840 minutes = 9:20 a.m.