Answer
$m=\frac{Ft}{V_2-V_1}$
Work Step by Step
To solve the given equation for $m$, we divide both sides by $V_2-V_1$ as follows
$$
Ft=m(V_2-V_1)\Longrightarrow \frac{Ft}{V_2-V_1}=\frac{m(V_2-V_1)}{V_2-V_1}\\
\Longrightarrow m=\frac{Ft}{V_2-V_1}
.$$
