A researcher synthesizes a new molecule called inhibitor X that inhibits the activity of phosphofructokinase (PFK), the enzyme that phosphorylates fructose 6−phosphate during glycolysis. Inhibitor X competes with ATP for binding to the PFK active site. The researcher determines that the Michaelis–Menten constant ( K m ) with respect to ATP is 40 µM. When 1.5 µM inhibitor X is added to the purified PFK reaction, the apparent K m for ATP increases to 52 µM. Calculate the dissociation constant of the PFK‑inhibitor complex ( K I ) .