Question $3$

Three rainfall stations recorded rainfall $($in mm$)$ from June to December, as shown below. During this time, the rain gauge at B recorded incorrect values. Plot a graph to find when the incorrect readings started to occur and calculate corrected values for that time, using the graph.

$\backslash$table$[[,$Station A$,$Station B$,$Station C$,$Ave AC$,$NEW,NEW$],[,$Rainfall,Rainfall,Cumulative,Rainfall,Rainfall,Cumulative,ACTUAL$],[$Jun$,130,125,,130,,,,],[$Jul$,140,140,,135,,,,],[$Aug$,150,145,,145,,,,],[$Sep$,130,100,,125,,,,],[$Oct$,140,110,,130,,,,],[$Nov$,145,115,,130,,,,],[$Dec$,125,95,,125,,,,]]$

When did the problem occur? $q,$

What is this method called? $q,$