When jp saw helene in the stockroom stuffing her purse with expensive printer cartridges, helene was quick to say, "we've been friends since first grade, so i'm sure you won't say anything about this." what influence tactic was helene using on jp?

Helen is using personal appeal.

Explanation:

Personal appeal is an influence tactic used by one individual to persuade another individual to take or not to take a certain action, in particular.  

Here, Helen is appealing to a personal fact, which bonds JP and Helen. By saying that they are friends since the first grade, Helen hopes to persuade JP into deciding that their friendship is more important than the act of theft. Perhaps, even that they might stop being friends if JP reports on her.

A personal appeal can be a very effective influence tactic if used smartly.

b) to encourage free trade