la 3 ) x/y=z/t  =>  xt=yz ; 9+xt/yz=9+1=10 4) 1/y=z/t =>t=zy => t=20 5) 25x=24y => x=24y/25 => x/y=24/25 6) x/4=y/20 => x=4y/20 => x/y=4/20 => x/y=1/5