It doesn't require any calculations, really, just logic. Look, 4n = 4n wil be equal because they are the same numbers multiplied by the same variable - no matter the variable's value. However, if you subtract both values by different numbers, you won't get the same number:
To get 1 cup of sugar, u must add 1/8 by 8. now you have one cup of sugar. But to find out how much flour u need, u also need to multiply 1 3/4 by 8, which gives u 5 cups
