With reference to relevant legislation and case law, determine if the following scenarios give rise to income for tax purposes:

a) John is a pensioner and swapping his surplus free range eggs valued at $150 (for the year) with his neighbour Alex for surplus vegetables grown in his home garden.

b) David is a builder and helping John at weekends to build his home, doing so on the basis that David can have Johns caravan towed trailer (which cost him $10,500 on 1 January 1997) when John move into his current home. Assume the value of the Davids work was $11,000 and the caravan had a market price of $12,000 when John handed it over on 1 January in the current income year.