Answer:
Marta predicted correctly 6 out of 13 football games .
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {6}{13}}\times 100 [/tex]
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {600}{13}}[/tex]
[tex]\longrightarrow[/tex][tex]\sf 46.15\% [/tex]
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {6+x}{13+x}}={\dfrac {65}{100}} [/tex]
[tex]\longrightarrow[/tex][tex]\sf 100 (6+x)=65 (13+x)[/tex]
[tex]\longrightarrow[/tex][tex]\sf 600+100x=845+65x [/tex]
[tex]\longrightarrow[/tex][tex]\sf 100x-65x=845-600 [/tex]
[tex]\longrightarrow[/tex][tex]\sf 35x=245 [/tex]
[tex]\longrightarrow[/tex][tex]\sf x={\dfrac{245}{35}}[/tex]
[tex]\longrightarrow[/tex][tex]\sf x=7 [/tex]
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {6+x}{13+x}}[/tex]
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {6+7}{13+7}}[/tex]
[tex]\longrightarrow[/tex][tex]\sf {\dfrac {13}{20}}[/tex]
[tex]\therefore [/tex] Marti needs to predict more 13 games out of 20 to raise her percentage to 65%.