Some people are obsessed about the idea of dropping metallic sodium into water. Assuming thumb sized lump weights 5.00 g, how much sodium hydroxide Jdurg added to the lake throwing three such sodium pieces?

This question looks boring easy. Let's start with the balanced equation and use ratios:

Note that both 45.98 g and 79.99 g are masses of two moles of Na and NaOH respectively, as such are amounts of substances taking place in the reaction. So proportion is

45.98 g : 79.99 g = 5.00 g : x g

and x = 79.99/45.98×5.00 = 8.70 g

Ready? No! There were three pieces dropped into the lake, so the final answer is 26.1 g.

(try to do this question using EBAS).