In 10 years, we can tell that the amount of fish increased by 1.833...(990 divided by 540) times. If we divide 1.833... by 10, we can find how much the pond increases by yearly. we get 0.1833... If we multiply that by 7 (because the gap between 1986 and 1979 is 7 years), we get 1.2833... So, if we multiply 540 by 1.28333..., we get 693 fish.
