Implement formulas for Dietela quiz item 9-15
- Added tests for formulas used in item 9-15
- Implemented formulas used in item 9-15
- Reformatted some formulas to make error messages more informative
@wulanmantiri @doanandreas18 @kefas.satrio @muzakiazami pls review yaa tqtq
Edited by Glenda Emanuella Sutanto