In the diagram below, D is the circumcenter. If BD = 7a - 4 and CD = 4a + 11, what is the length of AD?

Iam so stuck. what is the worked out answer for this question?

In the surface area formula for cylinders which expressionrepresents the lateral area

Asurvey of 45 teens found that they spent an average of 25.6 hours per week in front of a screen (television, computer, tablet, phone, based on the survey’s sample mean, which value could be the population mean? 2.3 hours 27.4 hours 75.3 hours 41.5 hours