Solve the system of equations. If the system has an infinite number of solutions, express them in terms of the parameter z.

{15x+4y+4z=360x+28y8z=1530x8y+4z=3\displaystyle {\left\lbrace\begin{array}{ccccccc} -{15}{x}&+&{4}{y}&+&{4}{z}&=&-{3}\\-{60}{x}&+&{28}{y}&-&{8}{z}&=&{15}\\{30}{x}&-&{8}{y}&+&{4}{z}&=&-{3}\end{array}\right.}

x=\displaystyle {x}=   
y=\displaystyle {y}=   
z=\displaystyle {z}=