Basic math question

[MrMoo]

For some reason I can't wrap my head around this.

From an article I'm reading:
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$3/6 heads-up game. Blinds $1/$3. To steal, the small blind raises $5 to win $4. Using simple arithmetic, we calculate that the preflop raiser needs to steal the blinds 55% of the time to make an immediate profi

[/ QUOTE ]

What is the "simple arithmetic" needed to figure this out? How do you get that 55%?

Thanks.