Step-by-step explanation:
The law of conservation of mass states that in a closed system, matter can neither be created nor destroyed. This means that the total mass of substances before and after a chemical reaction must remain the same. Therefore, for your given equation of 60g + 40g = 100g, we can see that the law of conservation of mass has been upheld as the total mass before (60g + 40g) and after (100g) the reaction is the same.