A scientist isolates $25$ grams of krypton-91, which decays according to the formula $$N(t) = 25e^{-0.07t}\text{,}$$ where $t$ is in seconds.

1. Complete the table of values showing the amount of krypton-91 left at $10$-second intervals over the first minute.

   $t$	$0$	$10$	$20$	$30$
   $N(t)$

   $t$	$40$	$50$	$60$
   $N(t)$

2. Use the table to choose a suitable window and graph the function $N(t)\text{.}$
3. Write and solve an equation to answer the question: How long does it take for 60% of the krypton-91 to decay?
   $25e^{-0.07t}= 0.60$
   $25e^{-0.07t}= 0.60 (25)$
   $25e^{-0.07t}= 0.40$
   $25e^{-0.07t}= 0.40 (25)$
   None of the above
   Answer: $t=$ seconds