So, the first cake needs x cups of flower. The second x+1/2 and the third 2x
in total this is x+x+1/2+2x=4x+1/2.
this is equal to
8/1/2
soo

4x=8
x=2
this is the first cake, the second will have 2
and the last one twice as much as the first, so 4
let's check
2+2.5+4=8.5 correct!