[tex]6\ cups\ of\ water\ for\ 4\ cubs\ of \ flour\\\\
x\ cups\ of\ water\ for\ 6\ cubs\ of \ flour\\\\making\ proportion\\\\
6-4\\x-6\\\\cross\ multiplication\\\\
6*6=4x\\\\
36=4x\ \ \ \ | divide\ by\ 4\\\\
x=9\\\\
9\ cups\ of\ water\ should\ be\ used.[/tex]