I need help with a chemistry question!!!?

Question

Here is the question:

You take a wooden painting to a local university for testing to find out the age. Living wood shows a carbon-14 activity of 15.3 counts per minute per gram. Your painting showed a carbon-14 activity of 15.1 counts per minute per gram. What age is the painting?

Answer 1

Assume t-1/2 of C-14 = 5720 yr (Your book may assume a different value. Just plug that one in.)

k = 2.3Log2/t-1/2 = 0.693/t-1/2

k = 1.21 x 10^-4

Log(15.3/15.1) = kt/2.3 = (1,.21x10^-4)(t)/(2.3)

(15.3cpm)/(15.1cpm) = 1.013; Log 1.013 = 0.005714

t = (2.3)(0.005714)/(1.21x10^-4)

t = 1.1 yr old.