What is $Strigula$?

If the lines $3x + 4y - 14 = 0$ and $6x + 8y + 7 = 0$ are both tangents to a circle,then its radius is

Particles of masses $m, 2m, 3m, \dots, nm$ grams are placed on the same line at distances $l, 2l, 3l, \dots, nl$ cm from a fixed point. The distance of the centre of mass of the particles from the fixed point (in cm) is

Pheromone is

Silviculture is the cultivation of which of the following?

The radius of the circle $r = 12 \cos \theta + 5 \sin \theta$ is