What is synthetic a priori cognition?

What is synthetic a priori cognition? How, basically, does Kant explain the possibility of such cognition? Discuss an example (either from the transcendental aesthetic or the analogies of experience), and identify the primary philosophical cost of Kant’s approach.Please use a good number of in-text citations from book “Modern Philosophy: An Anthology of Primary Sources, 2nd Edition” by Roger Ariew and Eric Watkins in addition to outside sources.