Answer:
[tex]\large\boxed{\sqrt{16}}[/tex]
Step-by-step explanation:
[tex]\sqrt{15}\ \text{is irrational number}\\\\\sqrt{21}\ \text{is irrational number}\\\\\sqrt{22}\ \text{is irrational number}\\\\\sqrt{16}\ \text{is rational number because}\ \sqrt{16}=4[/tex]
