Physics help please stuck :( physics please?

1)))---,Jean camps beside a wide river and wonders how wide it is. She spots a large rock on the bank directly across from her. She then walks upstream until she judges that the angle between her and the rock, which she can still see clearly, is now at an angle of 30° downstream (Figure 1-17). Jean measures her stride to be about one yard long. The distance back to her camp is 72 strides. About how far across, both in yards and in meters, is the river?

yards??

m??

2))-- A typical adult human lung contains about 290 million tiny cavities called alveoli. Estimate the average diameter of a single alveolus. Assume the alveoli are spherical and a typical human lung is about 1.9 liters.

___ m??

3))

Global positioning satellites (GPS) can be used to determine positions with great accuracy. The system works by determining the distance between the observer and each of several satellites orbiting Earth. If one of the satellites is at a distance of 22,000 km from you, what percent accuracy in the distance is required if we desire a 6 meter uncertainty?

_____%?

How many significant figures do we need to have in the distance?