Your application needs to perform 5 million writes and 5 million strongly consistent reads per day with item sizes of 5.5 KB:

Number of writes per day = 5,000,000
Number of writes per second = ceil (5,000,000 / (24 * 60 * 60))  = 58
1 WCU is required for each 1 KB of write. So, writes required for each item = ceil(5.5) = 6
Total WCU required  = 58 x 6 = 348
Similarly 5,000,000 strongly consistent reads per day  = 58 strongly consistent reads per second.
1 RCU is required for 1 strongly consistency read. So RCU required for 58 strongly consistent reads  = 58
1 RCU is required for 4KB of read. So reads required for each data item = ceil(5.5/4) = 2
Total RCU required = 58 x 2 = 116