Calculate the values of g at Earth's surface (in m/s²) for the following changes in Earth's properties:
(a) If its mass is tripled and its radius is quartered, the value of g is X m/s².
(b) If its mass density is tripled and its radius is unchanged, the value of g is 29.4 m/s².
(c) If its mass density is quartered and its mass is unchanged, the value of g is X m/s².