Shanna writes the formula f(x + 1) = 2.5f(x) when f(1) = 2 to represent this sequence: 2, 5, 12.5, 31.25, …

Which error did Shanna make?
A sequence has a common ratio of Three-halves and f(5) = 81. Which explicit formula represents the sequence?

f(x) = 24(Three-halves) Superscript x minus 1
f(x) = 16(Three-halves) Superscript x minus 1
f(x) = 24(Three-halves) Superscript x
f(x) = 16(Three-halves) Superscript x

She used the incorrect common ratio.
She used the incorrect initial value.
She should have multiplied by f(x) rather then have it as an exponent.
She treated the sequence as geometric instead of arithmetic.