score:3
Simple linear interpolation would produce an estimate of 1,499,000,000.
1,265,000,000 +3/5*(1,656,000,000-1,265,000,000) = 1,499,600,000
Since we only have 4 significant figures in the input data, and an exponential curve is going to be a little under a straight line, we should round down the 6.