Start by adding up the total sales in 2011 and 2012. You can make approximate estimates for the bars that are between lines. Since everything is in millions, you can ignore the 6 zeros behind every number to speed up your calculation:
1) In 2011, Asia sold 250, America sold 325, Europe sold ~210, Africa sold 150. The total in 2011 was 250+325+210+150 = 935.
2) In 2012, Asia sold ~130, America sold ~280, Europe sold ~230, and Africa sold ~140. The total in 2012 was 130+280+230+140=780.
Now find the percent decrease. Percentage decrease is basically what percent of your original number was subtracted from that original number to get the new number.
Percent decrease is calculated by (1) calculating the decrease from original number-new number, then (2) dividing that decrease by the original number, and then (3) multiplying your quotient by 100% to get a percentage:
1) Your original number is 935, from 2011, because that's the year you started out with. Your final number is 780, from 2012. The decrease is: 935-780 = 155.
2) Divide 155 by your original number. 155/935 ≈ 0.17
3) Finally multiply your quotient from step 2 by 100% to get your percent decrease: 0.17*100% = 17%.
The answer is A) 17.