John is twice as old as mary. the sum of their ages is 21. how old is mary? let j = john's age and m = mary's age. select the system equations that represent the problem.

J = 2M

J + M = 21

Step-by-step explanation:

M = Mary's age

J = John's age

"John is twice as old as Mary."

J = 2M

"The sum of their ages is 21."

J + M = 21

The system of equations is:

J = 2M

J + M = 21

answer: 32.68

step-by-step explanation:

x=2

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.