Can l get the solution by using arithmetic mean method $.?$A drainage basin boundaries can be represented by a polygon whose vertices are located in the following coordinates: $(5,5),(-5,5),(-5,-5),(0,-10)$ and $(5,-5).$ The rainfall amounts of a storm were recorded by nine rain gauges situated inside and outside the basin as follows:

$\backslash$table$[[$Gauge number,Coordinates,Recorded rainfall $($mm$)],[1,(7,4),62],[2,(3,4),59],[3,(-2,5),41],[4,(-10,1),39],[5,(-3,-3),105],[6,(-7,-7),98],[7,(2,-3),60],[8,(2,-10),25],[9,(0,0),81]]$