first subtract how tall is was 7 1/2 years ago from hell with all it is now. 57 - 40.5 = 16.5 or 16 1/2 so and the seven and a half years the tree Grace 16.5 with 16 1/2 seats to get the average yearly growth for the 7 1/2 year. You have to divide 16 and 1/2 ft by 7 and 1/2 Tim Wiles it makes it much easier if you change the fractions to decimals