84,600,600 write each number in scientific notation i have a dew more questions but im stuck 12points

Need on this geometry question. explain how you did it.

Two cyclists 84 miles apart start riding toward each other at the same. one cycles 2 times as fast as the other. if they meet 4 hours later, what is the speed (in mi/h) of the faster cyclist?

45% of the trees in a park are apple trees. there are 27 apple trees in the park. how many trees are in the park in all?