According to one source, the average of the annual mean temperatures for a thirty-year period in barrow alaska, was - 12.6*c which point on the number line is closest to -12.6*c

L is the closest to -12.6. It's obvious to see that every unit (1) on the number line is divided into five segments, so that each small segment represents 1/5=0.2. We know that -12.6 is between -12 and -13. -12.6 is 0.6 farther to the left than -12 (since -12.6 more negative), so we count 0.6/0.2=3 segments to the left of -12, corresponding to point L on the number line.