Please help cba to work it out myself

Identify the type of observational study described. a statistical analyst obtains data about ankle injuries by examining a hospital's records from the past 3 years. cross-sectional retrospective prospective

In need of in the diagram, ∠abc is a right angle. ∠dbc = 30°27'40". find the measure of ∠abd.

An arithmetic series a consists of consecutive integers that are multiples of 4 what is the sum of the first 9 terms of this sequence if the first term is 0