The first step is canceling out the like term, in this case it is the atoms and mole specification. I use e instead of multiplying times 10 to a power, it is mostly used in higher sciences but I think it is easier and it is in most calculators. So your equations is 7.43e22 Mg multiplied by (1/6.02e23) multiplied by (24.30) Mg. So all together it is 7.43e22 (1/6.02e23) (24.30). Then just multiply across, it is easier to break it up. 7.43e22 times (1/6.02e23)= .1234219269. Take that and multiply it by 24.30. So that looks like (0.1234219269)x(24.3)= 2.999152824. So if it would be 2.9992 grams of Mg.