I have a radio field (field ID=142) with 3 options: 1,2 and 3. I would like to show a number field below, which dynamically

• displays 0 if option1 is selected, 
• displays 77 if option2 is selected, 
• displays 99 if option3 is selected.

Rather than using javascript or php, I would like to use a formula as found here like ([142] = 1) ? 0 : ([142] = 2) ? 77 : 99 that is inserted as the default value (calculation -> math) field setting of the number field. Unfortunately, this returns an error ("invalid left-hand side in assignment") and doesn't work.