5 3/4 is the same as 15/4
3 1/2 is the same as 3/2
Divide 15/4 by 3/2
you can do this by flipping the fraction in the denominator and multiplying the two fractions
15/4 × 2/3
multiply you numerator and your denominators to make
30/12
you can simplify this by dividing top and bottom by 6
5/2
So for every month this tree's average growth is 5/2 feet