The question is how many ounces (dry material) to add to one gallon of water?
Formula given was 45.5g/100ml
45.5 grams (dry)= powdered sodium carbonate
100 ml (fluid)= water
The question is how many ounces (dry material) to add to one gallon of water?
Formula given was 45.5g/100ml
45.5 grams (dry)= powdered sodium carbonate
100 ml (fluid)= water
You need to convert $100$ml $= 0.1$ liter to its equivalent value in gallons. And you need to convert $45.5$ grams $= 0.045$ kilograms to its equivalent value in pounds (then multiply the value in pounds by 16 since there are 16 ounces per pound).
For help to convert from liters to gallons, and from kilograms to pounds, see these handy metric conversion tables.
Then divide the value you get in ounces by the value you get in gallons, and you'll have computed the number of ounces of dry material to add to one gallon of water.
$$\dfrac{x \;\text{ ounces}}{y\;\text{ gallons}} = \;\;\text{ounces needed per gallon.}$$