let

p = the aircraft's speed in still air

w = the speed of the wind

t1 = 6 hour with the wind

t2 = 7 hours against the wind

the speed of the plane traveling against the wind is: p - w

the speed of the plane traveling with the wind is: p + w

the speed of the plane in still air is thirteen times the speed of the wind

p = 13w

since speed = distance/time => distance = speed*time

traveling with the wind

d = (p + w)t1

traveling against the wind

d = (p - w)t2

so we can write

(p + w)t1 = (p - w)t2

(p + w)6 = (p - w)7

6p + 6w = 7p - 7w

p = 13 w

again we get the same equation as above and we can only conclude that is the speed of the wind is w then the speed of the plane in still air is 13w.

It is possible that some data is missing in the text of the problem.