Question

Identify the initial amount a and the growth factor b in the exponential function.

f(x) = 920 * 1.6^x

Answer 1

so where you have missed the a and the b ? - or in this mathbook the text of this exercise is the same ?

Answer 2

initial amount \(a\) is found by evaluating \(f(0)\), or by inspection
growth factor \(b\) is the base of the exponential function

See http://www.regentsprep.org/regents/math/algtrig/atp8b/examplesexponentialfunction.htm
for some discussion