The following table gives the national income and the population of a country for the years 1984 - 85 to 1989 - 90.

Year	National Income (in crores)	Population (In crore)
1984 - 85	Rs. 229.225	74.0
1985 - 86	Rs. 261.174	75.0
1986 - 87	Rs. 291.556	77.0
1987 - 88	Rs. 329.200	78.5
1988 - 89	Rs. 389.500	80.0
1989 - 90	Rs. 434.500	81.5

What was the average national income (in crores) for the years 1987 - 88, 1988 - 89 and 1989 - 90?