(policy letter provides illustration of how the "10 and 10" requirement of the capital gain exclusion functions when taxpayer owns business real estate in one entity and operates the business in another entity; IDOR says that taxpayers can exclude gain on sale of the business real estate (or entire business) that is held for 10 years and is used in the business in which the taxpayer materially participates for 10 years; letter notes that IA follows I.R.C. Sec. 469 rules for determining material participation; letter notes that exclusion applies to taxpayer who is a non-resident and (in second scenario) owns real estate in different entity that in which material participation occurs; letter notes that I.R.C. Sec. 469 would deem net income from self-rental as non-passive).