sat-dog

Choice B is correct. Avery earns $10 per hour working at job A. Therefore, if she works a hours at job A, she will earn dollars. Avery earns $20 per hour working at job B. Therefore, if she works b hours at job B, she will earn dollars. The graph shown represents all possible combinations of the number of hours Avery could have worked at the two jobs to earn s dollars. Therefore, if she worked a hours at job A, worked b hours at job B, and earned s dollars from both jobs, the following equation represents the graph: , where s is a constant. Identifying any point from the graph and substituting the values of the coordinates for a and b, respectively, in this equation yield the value of s. For example, the point , where and , lies on the graph. Substituting 16 for a and 0 for b in the equation yields , or . Similarly, the point , where and , lies on the graph. Substituting 0 for a and 8 for b in the equation yields , or .

Choices A, C, and D are incorrect. If the value of s is 128, 200, or 320, then no points on the graph will satisfy this equation. For example, if the value of s is 128 (choice A), then the equation becomes . The point , where and , lies on the graph. However, substituting 16 for a and 0 for b in yields , or , which is false. Therefore, doesn’t satisfy the equation, and so the value of s can’t be 128. Similarly, if (choice C) or (choice D), then substituting 16 for a and 0 for b yields and , respectively, which are both false.