Yuck!
The Roman numeral above is not a correct representation of an integer. But it takes some inspection to decide this. Decimal positional representation is clearly better.
You already know how decimal notation works (and probably would be happy to skip this topic).
324 means: 3 × 100 + 2 × 10 + 4 × 1 which is: 3 × 102 + 2 × 101 + 4 × 100
Remember that:
B0 = 1, no matter what number B is.
Fill in the blanks with the appropriate power of 10:
7305 = 7 × 10___ + 3 × 10___ + 0 × 10___ + 5 × 10___