A 52-year-old man from Delhi presents with fatigue and melena for 3 weeks. He denies any previous GI symptoms or weight loss. Hemoglobin is 8.5 g/dL, MCV 68 fL, RDW 18%. Serum ferritin is 8 ng/mL, serum iron 40 μg/dL, TIBC 440 μg/dL. Upper endoscopy reveals a bleeding gastric ulcer. After treatment of the ulcer, iron supplementation is started. Which of the following findings would indicate an adequate hematologic response to iron therapy at 4 weeks?