In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Patients had a mean age of 45 . 6 + / - 6 . 6 yrs and were 86 % black , 66 % male .
### Output Text:
Patients had a mean age of 45 . 6 + / - 6 . 6 yrs and were 86 % black , 66 % male . 