The credit of $28 means the money increase by $28 so it is expressed as
[tex]+28[/tex]
200 feet above sea level means that
[tex]+200[/tex]
As height above sea level is postive.
The debit of $18 means decrease in money. So it is expressed as,
[tex]-18[/tex]
The temperature below zero is negative. So temperature 11 degree below zero is,
[tex]-11[/tex]
