If 2 tablespoons=1 cup, then the recipe contains 3/4 cup of sugar to 1 cup of cornstarch.
The ratio of cornstarch to sugar is 1/(3/4)=4/3, or 1 1/3 to 1.
Another way to look at it is to take 1/3 of 3/4=1/4, so increasing 3/4 by 1/3 is the same as adding 3/4 to 1/4 = 1 cup. There is 1/3 more cornstarch than sugar.
For 3/4 of sugar and 1/8 of cornstarch, the ratio is (1/8)/(3/4)=1/8*4/3=1/6 or 1:6 (cornstarch:sugar).