I don't understand it sorry
Answer:
Speed of the river =
km per hour
Step-by-step explanation:
Speed of the boat in still water = 4 km per hour
Let the speed of the river = v km per hour
Speed of the boat upstream = (4 - v) km per hour
Time taken to cover 6 km = 
=
hours
Speed of the boat downstream = (4 + v) km per hour
Time taken to cover 12 km =
hours
Since, time taken by the boat in both the cases is same,

6(4 + v) = 12(4 - v)
24 + 6v = 48 - 12v
12v + 6v = 48 - 24
18v = 24
v = 
v =
km per hour
I assume you want the original price?
(37.90/9)*10 = $<span>42.11.... </span>
Multiply 7 by 0.08 and you get $0.56. $0.56 is the tax. For other tax questions just multiply the price and the sales tax as the decimal.
Answer:














hope this helps
sorry, I don't know how solve the 12th one.
thanks.