Inverter has propagation delay of , AND, OR gates have propagation delay.
Initially A = 0, B = 1, C = 0.
For every A,B,C are updated to new values as shown below.
t=5 A = 1,B=1,C=0
Output of the circuit at t=25 and t=30 respectively:
Edit: A,B,C values are not changed after t = 15 nsec