How to convert Roman numerals into numbers 

Find the value of each symbol.
First subtract.
Then add.

Subtract because as you see in Roman Numerals Rules:
When 'left' is smaller and 'right' is bigger, subtract the left from the right-hand figure.

Remember : 
'I Value Xylophones Like Cows Do Milk'.
`I=1`,  `V=5`,  `X=10`,  `L=50`,  `C=100`,  `D=500`,  `M=1000`

Example 1

Example 2

Example 3

Example 4