I need some help with an assignment.

This is the specification of the replica allocation problem: Click image for larger version. 

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with
ti : expected number of retrieval queries from site i
ui : expected number of update queries from site i
cij : cost of answering retrieval queries from site i using replica at site j
c′ij : cost of answering update queries from site i using replica at site j
di : cost of storing replica at site i
I ⊆ S : subset of sites where R is replicated

Assume that there is a relation R in a distributed database system consisting of sites S = {S1 , S2 }.
The task is to find the best replica allocation scheme for R for the following costs: Click image for larger version. 

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The solution is: Store R on S2 only.

Unfortunately I don't know what to do with the given data. Could somebody please give me a hint?

Thank you!