7.34x10^22 kg can also be written as 0.0734 * 10^24 kg
Since both numbers are * 10^24, you can just add 5.97 + 0.0734 = 6.043. Then you have to add the * 10^24 giving you 6.043 * 10^24 kg
The ratio of Earth / moon is 5.97x10^24 / 7.34x10^22 = 81. The mass of the Earth is 81 times the mass of the moon.