First, let's calculate the moon's diameter, knowing that the diameter has double the radius length:
[tex]\begin{gathered} \text{radius}=1.77\cdot10^6 \\ \text{diameter}=2\cdot\text{radius} \\ \text{diameter}=2\cdot1.77\cdot10^6 \\ \text{diameter}=3.54\cdot10^6 \end{gathered}[/tex]Now, writing the result in standard form, we have:
[tex]\text{diameter}=3,540,000[/tex]