Question 829935

Why does this not follow normal rule? 25-t=15 
Is this because the varible is not first.
Please and explain the answer which should be 10.
Thanks.<pre><font face = "Arial" size = 3 color = "blue"> <b>What "normal" rule doesn't the solution for this equation follow?</font face = "Arial" size = 3 color = "blue"> </b>