What is the significance of the $ 300 check to Samantha (Chapter 14, 15, & 16)?
The $300 check to Samantha is significant because it shows us how harsh Norm can be. It's another development to add to his character's unlikability. It's also significant in how it displays Mira's attempt at solidarity. She wants to help another woman in need. Finally, it's significant that Mira couldn’t write the check herself. Perhaps Mira still has a ways to go when it comes to asserting her independence from Norm and men in general.
One significance of the $300 check to Samantha might be how it reinforces Mira's contempt for Norm. Even though she married him, Mira doesn't seem to think too highly of Norm. What does she call him? She labels him "a figure-headed husband." He's not so much a person with feelings and specific attributes. He's more of an object of scorn.
What perhaps makes him more scornful is that he acknowledges that he feels sympathy for Samantha. He says, "I feel very very sorry for Samantha." Yet he doesn't give Mira the money to give to her because of her husband. What does Norm call Samantha's husband? "A loser" and a "stupid bastard," among other things.
Why can't Norm just forget about Samantha's husband and help her out? Here, the $300 drives home the significance of Norm’s pettiness. So what if he hates Simp, shouldn't he set aside his feelings to help someone out in need? It's not like he needs the money. As Mira tells us, $300 is what Norm spends at his golf club.
Besides showing how unlikable Norm's character is, the check also shows us Mira's attempt at solidarity. She's trying to help another woman in a precarious situation. We might say it's a sign of Mira's feminism.
We might also say it's significant that Mira didn't just write the check herself. She doesn't go behind Norm’s back. She asks him to do it. If she just would've done it, Samantha would've had the $300. Her inability to bring herself to write the check might signify how hard it is for Mira to stand up to her husband and take action in a meaningful way. It could signify that Mira still has work to do with asserting her independence and autonomy when it comes to Norm and men in general.