A Patient Is Suspected of Having Severe Anemia $\frac{12}{18}$

A patient is suspected of having severe anemia.His hematocrit is 18%,reticulocyte count is 12%,and red blood cell count is 2.2 × 10⁶ cells/μL.A normal hematocrit is taken as 45%.Which of the following expressions should be used to calculate the patient's reticulocyte index?

A) (2.2 × 10⁶) × $\frac{12}{18}$
B) (2.2 × 10⁶) × $\frac{18+12}{45}$
C) 12 × $\frac{18}{45}$
D) 18 × 18 - 2.2 × 10⁶