The atomic mass of gallium is 69.72. The density of iron is 7.87. The atomic mass of iron is 55.847. Calculate the number of gallium atoms in one ton (2000 pounds) of gallium. (Enter your answer to three significant figures.)

the atomic mass of any elemet contains avogardo numberof atoms

In case of Gallium,

69.72 gram is atomic mass and it cotnains around 6.023*10^23 atoms of Gallium

but, 2000 punds = 907184.7 grams

907184.7 gram of gallium contains = 6.023*10^23 * 907184/69.72

= 79 * 10^26 atoms