3/4 all over 2/3 equal to x/1 cup
So 3/4 / 2/3 =x/1 now you can cross multiple so 3/4*1=3/4 then 2/3*x=2x/3 then you can solve for x.
3/4=2x/3 multiple 3 to both sides so the 3 cancels with the denominator of 2x
9/4=2x then divide by 2 to both sides to get x alone
9/8=x
1.125=x
So for every 1 cup of white sugar you need 1.125 cups of brown sugar.