Greetings!
We can solve this by creating an algebraic equation.
[tex]5/4=7/x[/tex]
Cross Multiply.
[tex]5*x=4*7[/tex]
[tex]5x=28[/tex]
Divide both sides by 5.
[tex](5x)/5=(28)/5[/tex]
The Answer Is:
[tex]x=5.6[/tex]
Seven cakes would cost $5.60.
Hope this helps.
-Benjamin