First step is to get the mass of water molecule in grams:
From the periodic table:
molar mass of hydrogen is 1
molar mass of oxygen is 16
molar mass of a water molecule = 2(1) + 16 = 18 gm
Now, to convert the gm into amu, all you have to do is multiply the gm you got by Avogadro's number as follows:
mass of water molecule = 18 x 6.22 x 10^23 = 1.1196 x 10^25 amu which is approximately 1 x 10^25 amu
Joshua saw the rising batter form the cake in the oven.
He saw that because of the reaction of baking soda/powder with the liquid in the batter.