p1=Plot[Sin[x],{x,0,30},
AxesLabel->{"t (s)","y(t) (m)"},
PlotLabel->"Multiple plots",
PlotStyle->{GrayLevel[0.7],Thickness[0.01]},
ImageSize->6.5*72,
BaseStyle->FontSize->16];
phi=0.3;
p2=Plot[Sin[x+ phi],{x,0,30},
AxesLabel->{"t (s)","y(t) (m)"},
PlotLabel->"Multiple plots",
PlotStyle->{GrayLevel[0.2],Dashing[{0.02,0.01}]}];
Show[p1,p2]