Write the Roman numeral for the following number: $245$

Write the Hindu-Arabic numeral for the following Roman numeral: 

$\mathrm{XCVIII}$

Write the Hindu-Arabic numeral for the following Roman numeral: 

$\mathrm{DCCCXXV}$

Write the Hindu-Arabic numeral for the following Roman numeral: 

$\mathrm{MDCXLIV}$

Write the number names of $3,04,80,594$ in the Indian system of numeration as well as in the international system of numeration.

Give a rough estimate as well as a closer estimate for the following:

$3793+415$