A block of mass 5 kg is held in equilibrium near a vertical wall by two light strings and a horizontal force of magnitude \(X\) N, as shown in the diagram. The two strings are both inclined at 60° to the vertical.

(a) Given that \(X = 100\), find the tension in the lower string.

(b) Find the least value of \(X\) for which the block remains in equilibrium in the position shown.