Find the current i1 through a branch connected to a node of an ac circuit, knowing that i1 enters the node and connected to the same node are three other branches carrying the currents:
i2 = 14.6 sin(377t - 15°) A, leaving the node,
i3 = 21.3 sin(377t + 30°) A, entering the node, and
i4 = 13.7 cos(377t + 15°) A, entering the node, respectively.