explain in your own words how you would determine the mass of a product in a chemical reaction (theoretical yield) if you know the mass of reactant.

I would use the following steps:

Write the balanced chemical equation for the reaction. Use the molar mass to convert the mass of the reactant to moles. Use the molar ratio of product:reactant from the balanced chemical equation to convert moles of reactant to moles of product. Use the molar mass of the product to convert moles of product to mass of product.

You can use the diagram below to remind you of the importance of the molar ratio in mass-mass conversions

You must get over the mole "hill" to make the conversion.