The Interest I after t years is given by I = Prt = P*0.02*t
Now its investment after t years is given by P + I and this should be equal to 2*P for the investment to double.
Hence, P + I = 2P. Solve for t.
Just make a scale for the diagram
like 1cm=10 km and by using it sketch the distance and with the help of a protractor draw according to the angles given but be very precise in your measurements draw a vector diagram and calculate the answer.