At the market, 8 batteries cost $10.
How much do 6 batteries cost?

$7.50

Step-by-step explanation:

1 battery costs 10/8=5/4 dollars

(5/4)*6=15/2

15/2=7.50

54 kilometers per hour

step-by-step explanation:

according to rules:

1 km = 1000 meter

which means that 1 meter = 1/1000 km

1 hour = 3600 second [ as 1 hour = 60 min = 60 *60 seconds ]

which means that 1 second = 1/3600 hour

therefore, 1 kilometer/hour =

thus to convert 15 meter per second to kilometer per hour, we multiply 15 to 3.6 kilometer/hour.

15 meter/second=   which is the required answer.