Average means adding total number of observations divided by no of observations. here, by adding all the sum of money which is earn by A,B and C which is equal to 2070 and number of observations is 3. by dividing 2070 with 3, 690 is the answer. so the average money earned by them in a ay is 690.

= 800+550+620/3

=2070/3

=690 answer