Given A is between Y and Z and YA = 2x, AZ = 16x, and YZ = 4x+56, find AZ.
Plsss help

Half-Life of Carbon-14 is 5,730 years
elapsed time = half-life * [log (bgng amt / end amt)] / log(2)
elapsed time = 5,730 * log (100 / 42) / log (2)
elapsed time = 5,730 * log  ( 2.380952381) / log(2)
elapsed time = 5,730 * 0.37675070961/ 0.30102999566
elapsed time = 7,171 years

Source:
http://www.1728.org/halflife.htm