37. What is the retardation  of a moving particle if the relation between time (t) and position (x) is $t=A{x}^2+Bx$, where A and B are appropriate constants.
[Ans. $\raisebox{1ex}{$2A$}\!\left/ \!\raisebox{-1ex}{${\left(2Ax+B\right)}^3$}\right.$]