Flour : sugar = (1/3) : (1/5) = 5 : 3 . . . . . . . . multiply the first ratio by 15 to eliminate fractions
The total of ratio units in the last representation is 5+3=8, so for a recipe of 16 cups, each ratio unit will stand for 16/8 = 2 cups.
Multiplying the ratio by 2 cups, we find Amanda will need
... 10 cups flour : 6 cups sugar
for her recipe.
What you could do it is. Start adding numbers and once you get close to
6 numbers See if you are close to 51 and switch around the numbers to make it equal 51 hope this helps