What type of t-values do you have? It depends on the T-test you ran to obtain the value, but if you have some values (such as the standard deviation of the samples, the sample size, etc.) and know what test was run to obtain the t-value (e.g. a one sample t-test), I think you could just set up an algebra equation to obtain the mean. If you don't have any of the other information, I am at a loss. If you are comparing the two groups of samples, than you should have only 1 t-value.