Johnson, an elderly and illiterate man, lived with his nephew, Barker, and was dependent on him for support and assistance in all matters. Barker told Johnson that it would be in Johnson's best interest to transfer a tract of land called Greenacre to Barker for unspecified "tax reasons". Based on Barker's assurances and repeated urgings, Johnson signed a contract selling Greenacre to Barker. Could Johnson later disaffirm the contract? If so, upon what grounds? EXPLAIN your answer FULLY