Match the type of gears with their most appropriate description

Type of gear
(P)$$\,\,\,\,\,$$ Helical
(Q)$$\,\,\,\,\,$$ Spiral Bevel
(R)$$\,\,\,\,\,$$ Hypoid
(S)$$\,\,\,\,\,$$ Rack and pinion

Description
1.$$\,\,\,\,\,$$ Axes non parallel a and non intersecting
2$$\,\,\,\,\,$$. Axes parallel and teeth are inclined to the axis
3.$$\,\,\,\,\,$$ Axes parallel and teeth are parallel to the axis
4.$$\,\,\,\,\,$$ Axes are perpendicular and intersecting and teeth are inclined to the axis
5.$$\,\,\,\,\,$$ Axes are perpendicular and used for large speed reduction
6.$$\,\,\,\,\,$$ Axes parallel and one of the gears has infinite radius

One tooth of gear having $$4$$ module and $$32$$ teeth is shown in the figure. Assume that the gear tooth and the corresponding tooth space make equal intercepts on the pitch circumference.

The dimensions $$' a '$$ and $$' b '$$ respectively, are closest to

A gear set has a pinion with $$20$$ teeth and a gear with $$40$$ teeth. The pinion runs at $$30rev/s$$ and transmits a power of $$20KW$$. The teeth are on the $${20^ \circ }$$ full-depth system and have a module of $$5mm.$$ The length of the line of action is $$19mm.$$

The center distance for the above gear set in $$mm$$ is

A gear set has a pinion with $$20$$ teeth and a gear with $$40$$ teeth. The pinion runs at $$30rev/s$$ and transmits a power of $$20KW$$. The teeth are on the $${20^ \circ }$$ full-depth system and have a module of $$5mm.$$ The length of the line of action is $$19mm.$$

The contact ratio of the contacting tooth is