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In this paper, we consider a finite geographic area with multiple mobile stations (MSs) uniformly distributed within the area and multiple candidate locations (CLs) for deploying base stations (BSs) and relay stations (RSs) to serve the MSs. For this network scenario, we study the joint optimal placement of BSs and RSs into those CLs, and MS and RS power allocations such that the sum-capacity of the network is maximized while the target data rate of each MS is achieved. In order to investigate the energy-efficiency trade-offs between deploying BSs and RSs, we provide an iterative algorithm which first maximizes the sum-capacity of the network by optimally deploying a certain number of BSs. Then, the algorithm decreases the number of BSs to be deployed optimally by one and continues deploying RSs until the same sum-rate is achieved. The process continues until the number of optimally deployed BS is 1 and the number of optimally deployed RSs is less than or equal to the total number of candidate RS locations. Our numerical results suggest that significant gains in terms of reduction of total transmitted power can be obtained by replacing BSs with RSs. However, this gain diminishes when the number of BSs became too small which makes the BS-RS and RS-MS distances too large for energy efficient communications.