In the xy-plane, the point (0,3) is the vertex of a certain right angle. If the sides of the right angle intersect the x-axis at the points (-4,0) and (b,0), what is the value of b?

Matt and Michelle are at the northwest corner of their school's football field, which is a rectangle 300 ft long and 160 ft wide. Matt walks in a straight line directly to the southeast corner of the field. If Michelle walks 180 ft down the west side of the field and then walks in a straight line directly to the southeast corner of the field, how many feet farther, to the nearest 10 ft, will Michelle walk than Matt?

Hardin argued that grazing land held in common (that is, open to any user) would always be used less carefully than private grazing land. Each rancher would be tempted to overuse common land because the benefits would accrue to the individual, while the costs of reduced land quality that results from overuse would be spread among all users. But a study comparing 217 million acres of common grazing land with
433 million acres of private grazing land showed that the common land was in better condition.
Which of the following, if true, and known by the ranchers, would best help explain the results of the study?

An annually conducted, nationwide survey shows a continuing marked decline in the use of illegal drugs by high school seniors over the last three years.
Which of the following, if true, casts most doubt on the relevance of the survey results described above for drawing conclusions about illegal drug use in the teen-age population as a whole?

Plague bacilli, the microorganisms that cause bubonic plague, are typically carried from rodents to humans by fleas. Although the bubonic plague epidemic that devastated Europe in the Middle Ages probably originated with certain species of plague-infected rodents from central Asia, the nomadic peoples of central Asia never contracted plague.
Therefore, since they undoubtedly had some contact with infected rodents, it is likely that these central Asian peoples had physiological immunity against plague bacilli.
Which of the following, if true, most seriously weakens the argument?