ANSWER
Sara is wrong that she need 9 cups of sugar for making the 3 cakes.
Reason
As given
Sara has a recipe for a cake
recipe calls for 3/4 cups of sugar for each cake i.e
[tex]one\ cake\ require\ \frac{3}{4}\ cups\ of\ sugar.[/tex]
now we calculated for the 3 cake.
[tex]three\ cake\ require\ sugar\ = 3\times\frac{3}{4}[/tex]
we get
[tex]i.e\ 3cake\ require\ \frac{9}{4}cups\ of\ sugar.[/tex]
Therefore Sara assumption is wrong
Hence proved