Dropdown list from api (firestore) with many option list not view all option

hi all
i am beginner
I need build app with calculator if select dropdown list some label with value sum to other value
ex :
dropdown 1 → option list
label : laser
value :100:
label:ceramic
value:150

dropdown 2 —>
label : floor
value :100:
label:wall
value:150

if select option from dropdown 1 → label : laser value :100
and select option from dropdown 2 → label:wall value :150

in text box formula ( sum(dropdown1.value , dropdown2.value)
total = 250

my problem is firestore structure for a database
I need to know how to build correct
I am build but can not access for all option list only view one option not all option