Adding multiple prices

Hello

I have a form with two dropdowns and a pay button.

The first dropdown has quantity values (10, 20, 40) and the second dropdown has prices ($80, $90)

I can’t add the value $90 to the already added $80 One-Time Amount. Is there an option to add that second price?

The problem is when I select the $90 dropdown and select 10 as quantity, the stripe amount always display the $800 instead of $900.