It is given that arm length is proportional to height of statue.
So let x be the height of statue so it follows:

It is also given that the actual height of statue is 88feet and 5 inches.
It is known that 1 feet is 12 inches so 88+5/12=88.4167 feet.
The difference in approximate and actual height is 3.0834 feet.
Hence the answeres are:
The approximate height of the statue is 85.3333feet.
The difference in approximate and actual height is 3.0834 feet.