$2\mathrm{.}2.$ The data below consist of the closing price of the common stock of the American Te and Telegraph Corporation on $10$ recent trading days.

$\backslash$table$[[$Time$($t$),$Price,,Time$($t$),$Price$],[1,$R$24\mathrm{.}10,,6,$R$22\mathrm{.}73],[2,23\mathrm{.}80,7,22\mathrm{.}60,],[3,23\mathrm{.}39,8,21\mathrm{.}76,],[4,22\mathrm{.}90,9,22\mathrm{.}14,],[5,22\mathrm{.}10,10,21\mathrm{.}69,]]$

a$.$ Using a five$-$period moving average, forecast the price of the stock for period $10.$

b$.$ What is the error of the forecast in #$1-$a$?$

c$.$ Using a five$-$period moving average, forecast the price of the stock for period $11.$

$[20]$