E= 1 - (T4-T1)
a(T3-T2)
SOLVE THE FORMULA FOR T1??
I going to guess this is what you mean.
$\displaystyle E=1-\frac{T_4-T_1}{a(T_3-T_2)}$
First we want to clear the fractions so multiply the equation by $\displaystyle a(T_3-T_2)$
$\displaystyle Ea(T_3-T_2)=a(T_3-T_2)-T_4+T_1$
$\displaystyle Ea(T_3-T_2)-a(T_3-T_2)+T_4=T_1$
$\displaystyle T_1=a(E-1)(T_3-T_2)+T_4$