Answer
$t_{1}=t_{2}-\displaystyle \frac{A}{vT}$
Work Step by Step
The goal is to isolate the wanted variable on one side of the equation.
Multiply with $\displaystyle \frac{(t_{2}-t_{1})}{T}$
$ T\times \displaystyle \frac{(t_{2}-t_{1})}{T}=\frac{A}{v(t_{2}-t_{1})}\times \displaystyle \frac{(t_{2}-t_{1})}{T}$
$ t_{2}-t_{1}=\displaystyle \frac{A}{vT}\qquad$ ... subtract $t_{2}$
$-t_{1}=\displaystyle \frac{A}{vT}-t_{2}\qquad$ ... multiply with $-1$
$t_{1}=t_{2}-\displaystyle \frac{A}{vT}$
