The rate of removal of Aspirin from the body is a first order reaction with a rate constant,k = 0.34/h

Question

How long does it takes for 87.5% of Aspirin to be removed from the body?

Answer 1

Calculate k.
k = 0.693/t_1/2
k = 0.693/0.34 = ?

Then ln(No/N) = kt.
Use No = 100
and N = 12.5 (that's 100%-87.5% = 12.5%)
k from above.
Substitute and solve for t(in hours).

Answer 2

How do you calculate k?