Parallel lines have equal gradients; the gradient is the coefficient of x. In this case, it is very straight forward as there is only one equation in the list that has the same gradient/x-coefficient as the one in the question, which is 2. The answer has to be the third option (y = 2x - 6) and sure enough, if you input the x-value 4 into the equation, you will get 2 as the y-value, so we know the line passes through the point (4, 2).
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.
