Revisit of the section 4 logic

Fulfilling the logic as set out in:

https://www.pivotaltracker.com/story/show/67565922

Copying it here for prevent context switching:

Scenario 1:
If demoted tenancy = Yes
4 a) = Blank (none checked)
4 b) = Blank (none checked)

Scenario 2:
If demoted tenancy = No
If only one tenancy agreement ('Start date of the tenancy...' date entered, but 'Date of the most recent tenancy...' is left blank as well as the radio button questions after it in the white box)
4 a) = NA
4 b) = NA

Scenario 3
If demoted tenancy = No
If more than one tenancy agreement = Yes
4 a) = Yes of No (depending on users selection
4 b) = Yes of No (depending on users selection