During a biology practical, two students investigate reaction time using a falling metre rule. Student A holds the rule vertically, and student B positions their hand ready to catch it at the 0 cm0\text{ cm}0 cm mark. When student A releases the rule, student B catches it as quickly as possible. The distance the rule fell before being caught was 19.6 cm19.6\text{ cm}19.6 cm. The distance ddd (in metres) that an object falls from rest under gravity in time ttt (in seconds) is given by the formula: d=12gt2d = \frac{1}{2} g t^2d=21gt2 where g=9.8 m/s2g = 9.8\text{ m/s}^2g=9.8 m/s2.
Calculate the reaction time ttt of student B. Show your working.
Name the human coordination system responsible for this rapid reflex action, and state one way its signal transmission differs from that of the endocrine system.