2. An investigation of the relationship between trafc ow x (10005 of cars per 24 hours) and lead content y of bark on trees near the highway (119/ g dry wt) yielded the data in the 7:1- and yz- columns below: a: y 8.3 227 8.3 312 12.1 362 12.1 521 17.0 640 17.0 539 17.0 728 24.3 945 24.3 733 24.3 759 33.6 1263