$D.\frac{450}{x+5}$

$(1$ point$)$

Salt water $is$ flowing into $an$ aquarium that contains pure water. The concentration $of$ salt $in$ the

aquarium, $c\frac{g}{L}t,in$ minutes, $is$ given $by$ the formula:

$c=\frac{6t}{40+t}$

When does the salt concentration $in$ the aquarium reach $3\mathrm{.}5\frac{g}{L}?$

$A.t=50$

$B.t=52$

$C.t=54$

$D.t=56$

$(1$ point$)$

When fully simplified, ignoring non$-$permissible values, $\frac{12x^{12}}{4x^3}\frac{x^8}{24x^6}is$ equal $to$

$A.72x^3$

$C.\frac{1}{72}{x}^3$

$B.\frac{1}{72}{x}^7$

$D.72x^7$