Sorry, you are right - i have missed that b somehow. I need new monitor or new glasses.
Looks OK with me. To make solution 2 in one step you will have to dilute 2000 ppm solution 4000 times - something like 0.025 mL diluted to 100 mL. Two steps looks more ogical.
Only thing that makes me wonder is that you used formula M1V1 = M2V2 - which suggests molar concentrations. ppm and ppb are not molar, they are usually weight/weight. But it doesn't matter as dilution calculation looks the same in this case.