The mass of radioactive material present, m$,$ in a sample of initial mass, m$0,$ is given by the equation:

dmdt$=$k$.$m

Obtain an equation for the decay of reactive material. If the half$-$life, t$(1)/(2),$ of the material is $51\mathrm{.}5$ years, find the proportion of material $($i$.$e m$/$m$0)$ left after $44$ years. Give your answer to three significant figures.