Answer
$ \varepsilon = 60V$
Work Step by Step
we have
$3.0A = \frac{\varepsilon} {R}.................(i)$
And
$2.0A = \frac{\varepsilon}{R+10} ........(ii)$
dividind $(i)$ by $(ii)$
$ 1.5 =1+ \frac{10\Omega}{R}$
$0.5 R = 10\Omega$
$R = 20\Omega$
substituting value of $R$ in $(i)$
$ \varepsilon = 3.0A * R = (3.0 * 20)V$
$ \varepsilon = 60V$
