Algebra can be used to work out any sum with an unknown. It can be used in real life when we need to solve a sum which involves an unknown, for example, figuring out the price of an item when we only have the total value.
Money is used in our daily lives to buy items and it involves calculating with decimal places. Mensuration is the measurement of geometric qualities. Mensuration is used to deal with the dimensions of objects like houses so that architects can build them.