Final answer:
The nurse should see the infant with failure to gain weight and a high lead level of 70 mcg/dL first. This is because the infant's failure to gain weight and high lead level indicate a potential health concern that requires immediate attention.
Step-by-step explanation:
The nurse should see the infant with failure to gain weight and a lead level of 70 mcg/dL first. This is because the infant's failure to gain weight and high lead level indicate a potential health concern that requires immediate attention. Lead exposure can lead to developmental delays, and the high lead level puts the infant at risk for lead poisoning. The nurse should prioritize addressing the infant's health and coordinating appropriate interventions to ensure the infant's well-being.