The first two terms of a geometric sequence are 2root 5 and 10. Find the third and forth terms in the sequence.

The answers were
Third term = 10 root 5
Forth term = 50

How do you do this? Step by step please.

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?