I'm not sure I'm understanding your question correctly. Is this a riddle or a mathamaticle problem? In the second case, are you working with Integers, with Real Numbers, or with that kinds of numbers exactly?
If its a riddle, both $$2$$ and $$3$$ are solutions, as $$2+3=5$$ and both two and three start with a "t".
If you work with real numbers $$5-\frac{5}{2} = \frac{5}{2}$$ , i hope you can say $$\frac{5}{2}$$ starts with $$\frac{5}{2}$$.
If you work with integers, the notation of 'starts with "t"' also makes sense, for example 14248 starts with 14. In that case there is no solution though. You can try out all small t, and it cant work with big t as 5-t and t have either the same number of digits but are not equal, or one starts with 9, one with 1.
Hope that answers your question.