What is the value of a 1951 US 10 dollar bill?

No offense, but your question is too vague. There are different series of the $10 bill. It also depends on the condition. But overall they are worth about $15, so you've just earned $5.

CorrectionPlease check your bill again and post a new, separate question. The US didn't print any bills of any denomination with a 1951 date. The nearest dates are 1950 and 1953, depending on the type and denomination.