[donmcronald]

They meant the user pays a 42% premium. If the developer needs to earn $70 they need to charge $100 on the App Store which is a 42% increase for the user. So if you’re talking about passing along those costs it’s +42% on every purchase.

[systemvoltage]

No! The supply-demand curve intersects at $100 and not $70. 70/30 split is an internal transaction and cost of doing business. No different than distributor cut if you’re selling physical products.

The customer paid $100. That is by definition the price. All costs are relative to the price. For example, sales tax or transaction fees.