Answer
a) $q_1$ and $q_2$ determines the electric flux through the Gaussian surface.
b) All charges i.e $q_1$, $q_2$ and $q_3$ produce the electric field that exists at the point P
Work Step by Step
a) Electric flux through a closed surface only depends on the charges enclosed by the surface.
Therefore, $q_1$ and $q_2$ determines the electric flux through the surface.
b) Electric field at a point is determined by all the charges present.
Hence, all charges i.e $q_1$, $q_2$ and $q_3$ produce the electric field that exists at the point P
