56.4 as a fraction in simplest form

How do you answer this question? (step by step)

Don't know how to find x given these segment lengths

A33 gram sample of a substance that's used to detect explosives has a k-value of 0.1473. n = noekt no = initial mass (at time t = 0) n = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days