$442.$ Create and manipulate a data frame.

i$)$ Create a 'data.frame' named $\text{'}$my$.$trees' that has the following columns:

'Girth $=c(8\mathrm{.}3,8\mathrm{.}6,8\mathrm{.}8,10\mathrm{.}5,10\mathrm{.}7,10\mathrm{.}8,11\mathrm{.}0)$

'Height $=c(70,65,63,72,81,83,66)\text{'}$

Volume $=c(10\mathrm{.}3,10\mathrm{.}3,10\mathrm{.}2,16\mathrm{.}4,18\mathrm{.}8,19\mathrm{.}7,15\mathrm{.}6)$

ii$)$ Extract the fifth observational unit.

iii$)$ Extract the 'Girth' column referring to it by name.

iv$)$ Print out a data frame of all the observations except for the last observation.