Explanation

(a) From Kirchhoff’s first law, in an electric circuit the algebraic sum of the currents meeting at any junction is zero,
$ie.,\ \ \ \ \ \ \sum i = 0$
∴ Taking inward direction of current as positive and outward as negative, we have
$1A - 3A - 2A + I = 0$
$\Longrightarrow \ \ \ \ \ I = 4A$