A line of best fit by eye

Draw a straight line that follows the overall trend through the middle of the points, with roughly balanced deviations above and below. Do not join consecutive points or force the line through the origin. Use the line for an estimate, acknowledging scatter.

At 4 hours, this reasonable line gives a score of about 4. Reading within the observed range is interpolation. Predicting well outside it is extrapolation and less reliable, because the relationship may change.

Different reasonable lines give slightly different estimates. A best-fit line drawn by eye is a model of a trend, not an exact equation satisfied by every observation.