Here two scenarios are compared: inhalation and exhalation. The conditions of the lungs, during these scenarios, are compared. We are given the volumes of lungs, pressure and other data to assist us.

Since there is no change in temperature of our body, as per the given problem here; we will use it to solve the problem.

Using the ideal gas law: PV = nRT

we can also write it as: T = PV/nR

since, temperature is constant in the two scenarios, we can compare them by using the equation for temperature as:

`(P_1V_1)/(n_1R) = (P_2V_2)/(n_2R)`

or, `(P_1V_1)/n_1 = (P_2V_2)/n_2`

where, P1 = 759 mm Hg, V1 = 4.2 L, n1 = 248.1 moles, P2 = 768 mm Hg and V2 = 1.8

Thus, `n_2 = (P_2V_2n_1)/(P_1V_1)`

substituting the values of variables in this equation, we get n2 = **107.59 moles**. Thus, even when we have exhaled as much as we can, our lungs would still hold about 107.59 moles of air.

Hope this helps.