a) how do normal cells get transformed into neoplastic cells?
b) differentiate between viral oncogenes and cellular oncogenes.

Dear student,
a) Normal cells become neoplastic when they lose the property of contact inhibition. 

• Cell growth and cell differentiation are two highly controlled and regulated. processes of our body. In cancerous cells, there is a breakdown of this control and regulation.
• Normal cells exhibit the property of contact inhibition. This property inhibits their uncontrolled growth on coming in contact with other cells. Cancer cells lose this property and hence, they just keep on dividing. This gives rise to masses of cells known as tumours.

b) Proto oncogenes or cellular oncogenes are normal genes which are present in the body and regulate growth and differentiation. Due to some modifications the proto oncogenes are activated and transformed into oncogenes.
Viral oncogenes are the genes present in genome of virus and have the potential to cause cancer when inserted in a cell.
  Regards