Mr$.$ Jose Castillo is a resident Filipino Citizen. He purchased a parcel of land in Makati City in $1970$ at a consideration of P$1$ Million. In $2011,$ the land, which remained undeveloped and idle, had a fair market value of P$20$Million. Mr$.$ Antonio Ayala, another Filipino citizen, is very much interested in the property and he offered to buy the same for P$20$ Million. The Assessor of Makati City re$-$assessed in $2011$ the property at P$10$Million.

a$)$ When is Mr$.$ Castillo liable for real property tax on the land beginning $2011$ or beginning $2012?$ Explain your answer.

b$)$ Is Mr$.$ Castillo liable for income tax in $2011$ based on the offer to buy by Mr$.$ Ayala? Explain your answer.

c$)$ Should Mr$.$ Castillo agree to sell the land to Mr$.$ Ayala in $2012$ for P$20$ Million, subject to the condition as stated in The Deed of Sale that the buyer shall assume the capital gains tax thereon, how much is the income tax due on the transaction and when must the tax return be filed and the tax be paid by the taxpayer? Explain your answer.