Compute all parts of given question:
Question: A boy uses a slingshot to launch a pebble straight up into the air. The pebble reaches a height of 33.0 m above the launch point 1.5 seconds later. Assume air resistance is negligible.
Part A: What was the pebble's initial speed (just after leaving the slingshot)?
Part B: How much time did it take for the pebble to first reach a height of 16.5 m above its launch point?
I need help to determine how much time it take for the pebble to first reach a height of 16.5 m above its launch point.