Making a Valid DTD - XML

I am trying to create a DTD in the following Exercise I found online, However I am a little stuck on Whether or not this is right.

Any help Would be appreciated:

Task: What I have Done:

<?xml version="1.0" ecnoding="UTF-8"?>
<!DOCTYPE sale [

    <!ELEMENT sale (client)>
    <!ELEMENT client (address, phone, email)>
    <!ELEMENT address (#PCDATA) #REQUIRED>
    <!ELEMENT phone (#PCDATA) #REQUIRED>
    <!ELEMENT email (#PCDATA) #REQUIRED>

    <!ATTLIST sale pid (#PCDATA) #REQUIRED>
    <!ATTLIST sale quantity (#PCDATA) #REQUIRED>

    <!ATTLIST client name (#PCDATA) #REQUIRED>
    <!ATTLIST client nin (#PCDATA) #REQUIRED>
]>

<sale>
    <client>
        <address>17 fdas house</address>
        <phone>023423424324</phone>
        <email>something@gmail.com</email>
        <sale pid="heello" quantity="1"/>
        <client name="A" nin="1231212312"/>
    </client>
</sale>