The position of a ball as a function of time is given by x $=(5\mathrm{.}1$ m$/$s$)$t $+(-11$ m$/$s$^2)$t$^2.$Find the average speed of the ball between t $=1\mathrm{.}0$ s and t $=2\mathrm{.}0$ s$.$ Express your answer to two significant figures and include appropriate units.