To take a percentage of a number out, simply do the follow:
Number x Percentage = Answer.
Therefore:
14,500x(90/100)=13,050
To find what percentage a figure represents of a total, do the following simple equation:
Figure/Total x100 = Percentage.
So for your Earthquakes, you have a total of:
Total = 90 + 20 + 5 + 1 = 116 Earthquakes.
4 to 5 -> 90/116 x100 = 78% to 2 sig. fig.
5 to 6 -> 20/116 x100 = 17%
6 to 7 -> 5/116 x100 = 4%
7+ -> 1/116 x100 = 1%
The same technique is used everywhere else, sample size divided by total multiplied by 100 gives percentage. Not multiplying by 100 gives you a ratio of 1 that it represents, 1 being 100% (a complete unit).
Therefore for part 1. of your question I would just do 14,500x0.9=13,050.
You'll probably see that 90/100 = 0.9 since 90% is identical to writing 90/100 or 0.9.