Answer:

Step-by-step explanation:
Given a geometric sequence, the nth term of the geometric sequence is obtained by using the formula:

If the eleventh term, 
and the common ratio, r=-2.
Then:

The explicit formula for the sequence is:

245= 5*7*7 :) so 5 and 7 are prime factors of 245 :)
3+4=7
7 x 8=56
There will be 56 airplanes :)Hope this helped!