If $Z=\frac{A}{A-B}$ and $A$ and $B$ are measured with an error $\Delta A$ and $\Delta B$ respectively, then relative error in $Z$, that is $\frac{\Delta Z}{Z}$ is equal to
(1) $\frac{\Delta A}{A} + \frac{\Delta A + \Delta B}{A-B}$
(2)$\frac{\Delta A}{A} - \frac{\Delta A - \Delta B}{A-B}$
(3)$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A-B}$
(4)$\frac{\Delta A}{A} - \frac{\Delta A + \Delta B}{A+B}$
