How do I create a mobile & web application from an excel file that does calculations based on user inputs (many tabs, columns & formulas)?

I have created a spreadsheet which has as few tabs with formulas (vlookups, arithmetic operators etc). Users just need to input 3 values (input field) and the excel will formulas will calculate 3 output fields. What I hope to achieve is to replicate this in a mobile & web application. I.e the user interface will just allow the user to key in 3 input values and the calculator will generate and display the 3 output values. All the calculations are done in the background and not seen by the user (in fact the excel file/formulas) should not be accessed by users). Would like to know how I can start or the direction to research on for this project. I have chanced upon apache poi, not sure if it is suitable for such application. I don’t think databases (eg SQL) will be suitable since my data is basically calculations which the cells are related to one another by formula (not independent unique records). I understand there are softwares out that which converts spreadsheets to app but it is too costly for my application.