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