So can you elaborate more , I understand like

There are three formula text fields which gives the number of days as output like

[Formula 1] = 12

[Formula 2] = 10

[Formula 3] = 14

On 4th field which is [Formula 4] , you need to add the 12+10+14 and show the sum as 36 in the last field .

Is this is what you are asking !!!