What are three things people can tell me about measuring tape

Write the complete balanced equation for the reaction between lead (iv) oxide (pbo2) and water (h2o).

Does anyone know a lot about how to: - calculate mass of magnesium metal - calculate the actual yield of magnesium oxide - calculate the theoretical yield of mgo - calculate the percent yield of mgo - determine the percent yield of mgo - determine the average percent yield of mgo i had to do an online lab and its asking these questions but i have no idea where to start or how to be able to find these things. i can post the chart of the data from the lab or if you can tell me exactly how i can find each.

Describe at least two advantages and two disadvantages of using hydropower as a source of energy.