How do i do these math probs on my home work?they are the ones i need help on.?

9:A fire fighter needs to estimate the height of a burning building. She estimates the length of her shadow to be 8 1/2 feet long and the length of the building's shadow to be 51 feet long. Find the height of the building if the fire fighter is 5 2/3 feet tall.

16:On an architect's blueprint, 1 inch corresponds to 12 feet. Find the length of a wall represented by a line 8 1/4 inches long on the blueprint. Round to the nearest tenth if necessary.

17:The scale on a map states that 1 centimeter corresponds to 50 kilometers. On the map, two cities are 0.9 cm apart. Find the actual distance.

18:It is recommended that there be at least 7 square feet of work space for every person in a conference room. A certain conference room is 20' by 12'. Find the maximum number of people the room can accommodate.

these are all (except 18) about similar triangles, so that the sides are in a common ratio.
her shadow/her height = building shadow/ building height.
81/2 / 5 2/3 = 51 / x
17/2 / 17/3 = 51 / x
3/2 = 51/x
3x=102
x=34

1"/12' = 81/2"/x'
x = 17/2 * 12 = 102'
1cm/50km = .9cm/x
x = .9(50km) = 45km

20 by 12 = 240 sq ft
240/7 = 34 +2/7 people
we can't fit person 35 in, so 34