Pls me guys asap for 4, 5, 6, and 7 (show ! ) + lots of points!

4)

12/16=21/b

multiply both sides by b
(12/16)b=21

now multiple both sides by (16/12)
b = 21 (16/12) =28

5)
rate is distance / time or time/distance

train travels 279 km per 1.5 hr =270/1.5
or
1.5 hr per 270 =1.5/27p

answer choice a and c matches that.
looking at choice C...270km/1.5hr=5hr/270km

looking at choice A.. 1.5hr/270km=5hr/k km

the units don't match for choice C so the

right answer is A

6)

1.5/270=5/k

multiply both sides by k
(1.5/270)k=21

now multiple both sides by (270/1.5)
k = (270/1.5)21= 900

7) 75 points per 6 game

75 points / 6 games

75/6=P/20

multiply both sides by 20
(75/6)20=P

P=250