A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount. The average (arithmetic mean) of the amounts in row i is $${R}_{i}$$ $$(1 \leq i \leq 5)$$. The average of the amounts in column j is Cj $$(1 \leq j \leq 4)$$. What is the average of all 20 amounts on the spreadsheet?
(1) $${R}_{1}+{R}_{2}+{R}_{3}+{R}_{4}+{R}_{5}={550}$$
(2) $${C}_{1}+{C}_{2}+{C}_{3}+{C}_{4}={440}$$