2 added 3 characters in body
source | link

may be another option

f1[t_] := Sin[9 Pi t/10];
f2[t_] := 2 Sin[7 Pi t/10];
data=Table[{t,If[f1[t]>0 && f2[t] > 0, Max[{f1[t],f2[t]}], 0]},{t,0,20,0.01}];
p1 = ListPlot[data, Joined -> True, Filling -> Axis,FillingStyle -> Green];
p2 = Plot[{f1[t], f2[t]}, {t, 0, 20},AxesLabel->{"weeks","affection"},Evaluated -> True];
Show[p2, p1]

enter image description here

may another option

f1[t_] := Sin[9 Pi t/10];
f2[t_] := 2 Sin[7 Pi t/10];
data=Table[{t,If[f1[t]>0 && f2[t] > 0, Max[{f1[t],f2[t]}], 0]},{t,0,20,0.01}];
p1 = ListPlot[data, Joined -> True, Filling -> Axis,FillingStyle -> Green];
p2 = Plot[{f1[t], f2[t]}, {t, 0, 20},AxesLabel->{"weeks","affection"},Evaluated -> True];
Show[p2, p1]

enter image description here

may be another option

f1[t_] := Sin[9 Pi t/10];
f2[t_] := 2 Sin[7 Pi t/10];
data=Table[{t,If[f1[t]>0 && f2[t] > 0, Max[{f1[t],f2[t]}], 0]},{t,0,20,0.01}];
p1 = ListPlot[data, Joined -> True, Filling -> Axis,FillingStyle -> Green];
p2 = Plot[{f1[t], f2[t]}, {t, 0, 20},AxesLabel->{"weeks","affection"},Evaluated -> True];
Show[p2, p1]

enter image description here

1
source | link

may another option

f1[t_] := Sin[9 Pi t/10];
f2[t_] := 2 Sin[7 Pi t/10];
data=Table[{t,If[f1[t]>0 && f2[t] > 0, Max[{f1[t],f2[t]}], 0]},{t,0,20,0.01}];
p1 = ListPlot[data, Joined -> True, Filling -> Axis,FillingStyle -> Green];
p2 = Plot[{f1[t], f2[t]}, {t, 0, 20},AxesLabel->{"weeks","affection"},Evaluated -> True];
Show[p2, p1]

enter image description here