As simple as that, you need only one credit that enables the complete generation of a quiz or test using AI. Same applies to the AI image generation.
However, if you are not fully satisfied with the generated result and want to make a small adjustment to your challenge, such as regenerating the question subject, an additional credit will be used. This does not apply to manual editing; credits are only used for AI-based generation.
Depending on your plan, you have a different amount of credits included in it. You can check your settings to understand how many credits you have left.