Is there more than one equation for Delta T(reaction)? So, I have to find the $\Delta T_{\mathrm{reaction}}$ of a solution for my lab report. Earlier in the lab, it gave the equation as 

$\Delta T_{\mathrm{reaction}}=T_{\mathrm{mixture}}+\frac{1}{2}(T_{\mathrm{substance~1}}+T_{\mathrm{substance~2}})$

and all temperatures were at the exact time of mixing found from a linear equation of temperature points on a graph. Now, I have another mixture which is water and a substance and I am supposed to find the $\Delta T_{\mathrm{reaction}}$. 

Here's the thing, we don't have the temperature of the substance, only the temp of the water and the solution it made, so how could I go about doing it? I thought about using room temperature since it was a solid substance but it doesn't say anything about that.

The substance is solid $\ce{NaOH}$.
If You are stating you have your initial water temperature and the final solution of your temperature, then your change in temperature is just your final temperature minus your initial temperature. No need for linear equations. The change in temperature for the reaction is the temperature change of the water due to the heat given off or absorbed by the system to the surroundings.