PLEASE HELP URGENT I'LL GIVE A LOT OF POINTS Find the explicit formula for the given sequence.

-4, 12, -36, 108,...

a
a_n=5·3^{n-1}

b
a_n=4·3^{n-1}

c
a_n=-4·(-3)^{n-1}

d
a_n=15·3^{n-1}

Marcus and cody both leave the park at the same time, but in opposite directions. if cody travels 6 mph faster than marcus and after 4 hours they are 64 miles apart, how fast is each traveling? solve using rare times time = distance.