In $1975,$ brothers Quincy and Ronald purchased a tract of real property as joint tenants with right of survivorship. Quincy contributed $$5,000$ toward the $$20,000$ purchase price and Ronald contributed the remaining $$15,000.$ When Ronald died in the current year, the date$-$of$-$ death value of the real property was $$100,000.$ The value of Ronald$$s interest in the real property includible in his gross estate under IRC $2040$ is:

$1.$

$$0.$

$2.$

$$50,000.$

$3.$

$$75,000.$

$4.$

$$100,000.$

$5.$

None of the above.