1. In the fourth A.D. about 140,000 tones of grain was imported each year
2. 1000000(peopleof Rome) divided by 140,000(tons of grain) = 7.14285714286 multiplied by 750,000(people of Alexandria) = 85,714 tons.
7.14285714286 multiplied by 250,000(people of Smyrna) = 28,572 tons
(I might be wrong so please if anyone could check my answer that would be nice)