If the inspiratory capacity (IC) of a person’s lungs is approximately 3,000 mL, and his functional residual capacity (FRC) around 2,300 mL, what would be the vital capacity of his lungs? Note that the residual volume (RV) is 1,200 mL.

Vital capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is the sum of inspiratory capacity (IC) and expiratory reserve volume (ERV). 
IC = 3,000 mL
FRC = 2,300 mL
RV = 1,200 mL
VC = IC + ERV 
Since ERV is not directly given, we need to find it from FRC and RV.
FRC = ERV + RV 
2,300 mL = ERV + 1,200 mL
ERV = 2,300 mL – 1,200 mL
ERV = 1,100 mL
Now, we can find vital capacity (VC):
VC = IC + ERV 
VC = 3,000 mL + 1,100 mL
VC = 4,100 mL