$(*$ select parts$)$ Assume that $x,y$ and $z$ are non$-$negative, continuous decision variables $($unless otherwise indicated$).$ Write constraints and answer any related questions:

a$)()$ I can kill a target with $10$ weapons type $x,$ or $20$ weapons type $y,$ or $30$ weapons type $z.$ What combinations of $x,y$; and $z$ can kill the target? $($Assume here that $x,y$ and $z$ are also integer, given they refer to a number of weapons$)$

e$)(*)$ A certain gasoline is produced by blending crude oils of types $x(0\mathrm{.}5\%$ lead content$),y(2\mathrm{.}0\%$ lead content$)$ and $z(3\mathrm{.}0\%$ lead content$).$ What mixtures of the three oils guarantee a gasoline with no more than $1\mathrm{.}5\%$ lead content?