Which equation has exactly ONE solution?

On saturday a souvenir shop had 125 customers.sixty four percent of the costumers paid with a credit card. how many costumers paid with cash?

My math teacher told my class to "steal" a 6th grade fraction word problem from the internet, word problems? : -p requirements: only a 1 step word problem. needs to be complex.

An ulcer medication has 300 milligrams in 2 tablets. how many milligrams are in 3 tablets?