in which of these situations do the quantities combine to make 0? A. A dolphin swims 20 feet straight down from the surface. It then rises 20 feet to return to the surface. B. Scott earns $20 at his family's garage sale. He then earns $20 walking dogs for his neighbors. C. Travis receives $10 from a friend to pay for a concert ticket. He then spends $20 on tickets for his friend and himself. D. A scuba diver drops 30 feet below sea level. He then swims 30 feet across the ocean floor.

A. A dolphin swims 20 feet straight down from the surface. It then rises 20 feet to return to the surface.

Step-by-step explanation:

It goes down 20 then up 20

-20 + 20 = 0

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.

47 - 90 = 43

43 - 180 = x

x = 137