During a marine biology study on the Weddell seal (Leptonychotes weddellii), researchers investigate the oxygen-binding properties of its skeletal muscle myoglobin compared to human adult haemoglobin.

The adult haemoglobin oxygen dissociation curve has the following reference points:

• At a partial pressure of ${pO}_2=3.6kPa$, human haemoglobin is $50\%$ saturated.
• At a partial pressure of ${pO}_2=5.4kPa$, human haemoglobin is $72\%$ saturated.
• At a partial pressure of ${pO}_2=9.0kPa$, human haemoglobin is $90\%$ saturated.

The oxygen dissociation curve for the seal's myoglobin is modelled as follows:

1. At low partial pressures, the oxygen saturation of myoglobin increases linearly from the origin $(0,0)$ at a constant rate of $12.5\%$ per $kPa$ of oxygen, up to a saturation level of $75\%$.
2. For higher partial pressures, the rate of oxygen binding slows down continuously until the myoglobin reaches $100\%$ saturation.
3. The partial pressure of oxygen at which myoglobin first reaches $100\%$ saturation is equal to the partial pressure at which human haemoglobin is $90\%$ saturated.

Based on this model: