PROBLEM $3-16$ Cost Behaviour; High$-$Low Method; Contribution Format Income Statement $[$LO$1,$ LO$2,$ LO$3]$

Skate World is a merchandising company that sells skateboards both at its retail store and its online store. Results for the most recent three months are shown below.

$\backslash$table$[[,$July,August,September$],[,4,000,4,500,5,000],[$Sales$,$$$400,000,$$$450,000,$$$500,000$