4. Two forces \(\mathbf { F } _ { 1 }\) and \(\mathbf { F } _ { 2 }\) act on a rigid body, where \(\mathbf { F } _ { 1 } = ( 2 \mathbf { j } + 3 \mathbf { k } ) \mathrm { N }\) and \(\mathbf { F } _ { 2 } = ( \mathbf { i } + 4 \mathbf { k } ) \mathrm { N }\). The force \(\mathbf { F } _ { 1 }\) acts through the point with position vector \(( \mathbf { i } + \mathbf { k } ) \mathrm { m }\) relative to a fixed origin \(O\). The force \(\mathbf { F } _ { 2 }\) acts through the point with position vector ( \(2 \mathbf { j }\) ) m . The two forces are equivalent to a single force \(\mathbf { F }\).

1. Find the magnitude of \(\mathbf { F }\).
2. Find, in the form \(\mathbf { r } = \mathbf { a } + \lambda \mathbf { b }\), a vector equation of the line of action of \(\mathbf { F }\).