4. The rate of decay of the mass of a particular substance is modelled by the differential equation $$\frac { \mathrm { d } x } { \mathrm {~d} t } = - \frac { 5 } { 2 } x , \quad t \geqslant 0$$ where \(x\) is the mass of the substance measured in grams and \(t\) is the time measured in days.
Given that \(x = 60\) when \(t = 0\),

1. solve the differential equation, giving \(x\) in terms of \(t\). You should show all steps in your working and give your answer in its simplest form.
2. Find the time taken for the mass of the substance to decay from 60 grams to 20 grams. Give your answer to the nearest minute.