Fifty identical thin hemispherical bowls have an outer radius of 30\,cm. Covering the curved outside of each bowl with iron sheet costs Rs 150 per m2, while aluminium sheet costs Rs 200 per m2. Ignoring wastage, what is the difference in total material cost between using aluminium and iron for all 50 bowls?
a) Rs 1\,130
b) Rs 2\,828
c) Rs 1\,414
d) Rs 707