In the following chart, the price of logs shown is per cubic meter and that of plywood and saw timber is per ton. Given that $1$ cubic meter of Plywood and Saw Timber = $800$ kg ($1$ ton = 1000 kg)
If $1$ cubic meter = $750$ kg for Saw Timber, in which year was the difference in prices of saw timber and logs the last?
- $1989$
- $1990$
- $1991$
- $1992$