If the current i$($t$)$i$($t$)$ for an element is $9\mathrm{.}2$t$9\mathrm{.}2$t A for t$0$t$0,$ and $7\mathrm{.}2$t$7\mathrm{.}2$t A for t$0$t$0.$

Find:

$($a$)$ i$(7\mathrm{.}9)$i$(7\mathrm{.}9)$

$($b$)$ i$(4\mathrm{.}9)$i$(4\mathrm{.}9)$

$($c$)$ The total charge that has passed through the element in the interval $7\mathrm{.}9$t$4\mathrm{.}97\mathrm{.}9$t$4\mathrm{.}9$

$($d$)$ The average current that has passed through the element in the interval $7\mathrm{.}9$t$4\mathrm{.}97\mathrm{.}9$t$4\mathrm{.}9.$