Answer
(a) $\langle 0, 0 \rangle$
(b) no additional force required.
Work Step by Step
(a) Given $\vec {F_1} =\langle 3, -7 \rangle$, $\vec {F_2} =\langle 4, -2 \rangle$, and $\vec {F_3} =\langle -7, 9 \rangle$, the resultant force acting at P is the sum of the forces $\vec {F} =\vec {F_1} + \vec {F_2} + \vec {F_3} =\langle 0, 0 \rangle$
(b) There is no additional force required since the total force is already zero.
