First, let's convert each dimension into inches:
[tex]\begin{gathered} 2.5ft\rightarrow30in \\ 1.75ft\rightarrow21in \end{gathered}[/tex]
Now, we can calculate the lenght to width ratio:
[tex]30\colon21\rightarrow10\colon7[/tex]
Now, we can use the dimensions of the cover and a rule of three to calculate our maximum width:
This way,
[tex]x=\frac{11\cdot7}{10}\rightarrow x=7.7[/tex]
Therefore, we can conclude that the picture on the cover should measure 11" by 7.7"
