Use a custom object to create the dropdown 

customObjects: 
  - id: TIME_DROPDOWN
    displayName: Time Dropdown
    customAttributes:
      list:
        - name: DAY
        - name: WEEK
        - name: MONTH

When selecting the data assign it to a variable, next all you need to  is put in a YAML code i,e, like 

${(VARIABLE === 'DAY' && 8 ) ||(VARIABLE ===   'WEEK' && 40)}

Depending on the use case you should be able to change the same accordingly 

Hi ​@abhishek.chatu14 ,

I am trying to build it in new studio views not in legacy views. How I can implement it using input dropdown.

Regards,

Ajith Naidu.

Similar approach you can use the Input dropdowns with manual input and assign the data to a variable, now use this vairable to do the calulations

Configuring user inputs (input box, input dropdown, button)