Final answer:
The number of igniters that fire on Manual or In-flight starts depends on the type of engine being used. One igniter fires on Manual or In-flight starts for the first type of engine, and no igniters fire on Manual or In-flight starts for the second type of engine.
Step-by-step explanation:
The number of igniters that fire on Manual or In-flight starts depends on the type of engine being used. According to the information provided, there are two types of engines mentioned: the first one fires at 3 s (green flame) and uses a liquid fuel/oxidant mixture, while the second one fires at 4 s (yellow flame) and uses a solid mixture. Therefore, one igniter fires on Manual or In-flight starts for the first type of engine, and no igniters fire on Manual or In-flight starts for the second type of engine.