Well first you have to subtract 2/3 by itself and to 1/2.
1/4t(2/3-2/3)=(1/2-2/3)
Then in order to get t by itself you have to divide 1/4 by itself and to the other side.
(1/4t / 1/4) = (-1/6 / 1/4)
t=-2/3
Hope this helps!