primer

/primer/

Cases

SingularPluralWhen to use it
nominativeprimerthe sumprimerlethe sumsthe plain dictionary form — the doer of the sentence
genitiveprimernithe sum'sprimerlenithe sums'the owner — whose it is
accusativeprimernithe sum (as the object)primerlenithe sums (as the object)a specific, known object — whom or what
dativeprimergeto the sumprimerlegeto the sumsdirection or recipient — to where, to whom
locativeprimerdeat / in the sumprimerledeat / in the sumswhere it is; also having — mende bar, "I have it"
ablativeprimerdenfrom the sumprimerledenfrom the sumswhere it comes from; also "than" when comparing
When to use each case
nominative
the plain dictionary form — the doer of the sentence
genitive
the owner — whose it is
accusative
a specific, known object — whom or what
dative
direction or recipient — to where, to whom
locative
where it is; also having — mende bar, "I have it"
ablative
where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
myprimerimmy sumprimerlerimmy sums
yourprimeringyour sumprimerleringyour sums
his / herprimerihis / her sumprimerlerihis / her sums
ourprimeribizour sumprimerleribizour sums
you all'sprimerigizyou all's sumprimerlerigizyou all's sums
theirprimerleritheir sumprimerleritheir sums

The overlap in the last rows is real, not a mistake: primerleri can mean "his / her sums", "their sum", or "their sums" — context decides.