Solve the following system of equations.

n= -6, a= 5

Step-by-step explanation:

Label the two equations:

a= -2n -7 (1)

-3a +n= -21 (2)

Substitute (1) into (2):

-3(-2n -7) +n= -21

Expand:

-3(-2n) -3(-7) +n= -21

6n +21 +n= -21

Simplify, minus 21 on both sides:

7n= -21 -21

7n= -42

Divide both sides by 7:

n= -42 ÷7

n= -6

Substitute n= -6 into (1):

a= -2(-6) -7

a= 12 -7

a= 5

54 km / hours

step-by-step explanation:

we need to convert seconds to hours

60 seconds = 1 minutes

60 minutes = 1hour

15 m         60 second   60 minutes

  * *         = 54000 meters/ hour

second     1 minute             1 hour

now we need to convert meters to km

1000 m = 1 km

54000 m       1 km

*   = 54 km / hours

hour               1000m