How to create a post sale email that calculates 5% of purchase subtotal?

Technical Q&A

Topic summary

Request to set up a post-sale email that computes 5% of the purchase subtotal. No platform or template engine specified, so implementation details are unclear. No solutions or steps provided yet; no decisions made. Discussion remains open with no attachments or media involved.

Summarized with AI on January 19. AI used: gpt-5.
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I’m trying to create a post sale email that takes the subtotal of their purchase and multiplies it by 5%. Appreciate any help. Thanks