In a test run, a certain car accelerates uniformly from zero to $22\mathrm{.}8$ m$/$s in $2\mathrm{.}15$ s$.$

$($a$)$ What is the magnitude of the car's acceleration?

$10\mathrm{.}6$ m$/$s$2$

$($b$)$ How long does it take the car to change its speed from $11\mathrm{.}4$ m$/$s to $22\mathrm{.}8$ m$/$s$?$