Distance between first tree and last tree is 140m .
And distance between each tree (d) = 5 m
let's solve for number of trees (n) :
[tex] \hookrightarrow \: (n - 1)d = 140[/tex]
[tex] \hookrightarrow \: (n - 1)5 = 140[/tex]
[tex] \hookrightarrow \: n - 1 = \dfrac{140}{5} [/tex]
[tex] \hookrightarrow \: n = 28 + 1[/tex]
[tex] \hookrightarrow \: n = 29[/tex]
hence, total number of trees = 29.