The function which represents the situation is:
[tex]\boxed{y=89000*(0.91)^t}[/tex]
where t is the time in years and y is the depreciated value of the motor.
In 4 yars value will depreciated to:
[tex]y=89000(0.91)^4\\
\\
y=89000(0.6857)\\
\\
\boxed{y=US\$ \ 61031.71}[/tex]
