Approach any anemia by cell size first, then iron studies. Here the $MCV$ is $68\,\text{fL}$, well below the $80\,\text{fL}$ lower limit, placing this in the microcytic category.
Among microcytic anemias, the serum ferritin separates them cleanly. Ferritin reflects total body iron stores; a low ferritin means the iron tank is empty, which is specific for iron deficiency. In thalassemia and anemia of chronic disease ferritin is normal or elevated, so a low value rules them out.
The distractors fail on size or stores: megaloblastic anemia is macrocytic (high $MCV$), aplastic anemia gives pancytopenia with normal/high ferritin, and hemolytic anemia is normocytic with high reticulocyte count, $LDH$ and bilirubin rather than a low ferritin. Everything converges on iron deficiency.
\[\boxed{\text{Low } MCV + \text{low ferritin} \Rightarrow \text{Iron deficiency anemia}}\]