$\text{a)}3\text{ha}=3\cdot 1\text{ha}=3\cdot 100\text{a}=300\text{a}$  

---

$\text{b)}14\text{ha}=14\cdot 1\text{ha}=14\cdot 100\text{a}=1400\text{a}$  

---

$\text{c)}900{\text{m}}^2=9\cdot 100{\text{m}}^2=9\cdot 1\text{a}=9\text{a}$  

---

$\text{d)}5000{\text{m}}^2=50\cdot 100{\text{m}}^2=50\cdot 1\text{a}=50\text{a}$