PLEASE HELP ON 13 TO BE MARKED THE BRAINLIEST

  D) 10000 feet

Step-by-step explanation:

We are told that for some actual altitude, the reading is ...

  30,000 ft = (1 -25%)altitude = 0.75×altitude

Multiplying by 4/3, we have ...

  (4/3)(30,000 ft) = altitude = 40,000 ft

To get to 30,000 ft, the plane must descend ...

  40,000 ft -30,000 ft = 10,000 ft

step-by-step explanation:

first, eliminate the parenthesis:

3

x

+

2

−

4

x

second, group like terms:

3

x

−

4

x

+

2

third, combine like terms:

(

3

−

4

)

x

+

2

→

−

1

x

+

2

→

−

x

+

2