Can you replace the question mark with a number?

A tourist, driving by a Texas ranch, hit and killed a calf that was crossing the road. The driver went to the owner of the calf and explained what had happened. He then asked what the animal was worth.

"Oh, about $200 today," said the rancher. "But in six years, it would have been worth $900. So $900 is what I'm out."

The tourist sat down and wrote out a check and handed it to the farmer.

"Here, is the check for $900," he said. "It's postdated six years from now."