You have four quantities Volts (V) ; Amps (I) ; Power (P) and Resistance (R). If you know any two of these you can calculate the other two using the formulae in you coloured diagram. So if you want to know the Volts you look in the brown quarter and one of the three formulae will equal the volts using the two other quantities you are given. Can you see which one you need from your question?