Superposition Principle and Continuous Charge Distribution

Four equal charges of value $+Q$ are placed at any four vertices of a regular hexagon of side $a$. By suitably choosing the vertices, what can be the maximum possible magnitude of electric field at the centre of the hexagon?

Eleven equal point charges, all of them having a charge $+Q,$ are placed at all the hour positions of a circular clock of radius $r$ except at the $10 \mathrm{h}$ position. What is the electric field strength at the centre of the clock?