Hey there! To find surface area, we need to cut this figure into 3 separate shapes (I included a link to help explain a little better). Once this is done, calculate the area of each one, using the formula length * height. Now, add up the area from each individual shape, and you've got the answer!
Seeing as there are 1582 sets of 100 people (158200 ÷ 100) multiplying 42 by 1582 should get you the answer. 1582 × 42 = 66444. 66444 people voted in that city.