Identity Property of Zero!
I hope this helps xD
Answer:
Speed of river's current = 5 mph
Step-by-step explanation:
Let 'd' be the distance covered
Let x be the speed of the rivers current
Speed upstream = 15-x
speed downstream = 15+x
Time = distance / speed
time upstream = 
time downstream = 
the ferry trip upstream takes twice as long as its return trip downstream
= 
divide both sides by d
= 
cross multiply


Add 2x on both sideds

subtract 15 from both sides and divide by 3

x=5
Speed of river's current = 5 mph
400, if you can buy 4 tickets for $6 you can buy 400 for $600
Answer:
B) 131°
Step-by-step explanation:
-4a + 139 = 4a + 123 because they are vertical angles
-4a + 139 = 4a + 123
reduce:
8a = 16
a = 2
4(2) + 123 = 131°