Answer
Find out the how much did the height of the tree sapling increases.
To proof
Let us assume that the height of the tree sapling increases be x.
As given
The high every tree sapling was 3.15 inches last year
this year the high is 5.38 inches.
than the equation is become in the form
x = 5.38 - 3.15
x = 2.23 inches
Therefore the height of the tree sapling increases be 2.23 inches.
Hence proved