They could have assembled total 336 different possible crews.
Explanation
Total number of trained pilots is 9 and geologists is 4.
The crew should be consisted of 2 pilots and 1 geologist. That means, 2 pilots are chosen from total 9 and 1 geologist is chosen from total 4.
Number of ways for choosing 2 pilots from 9 [tex]= ^9C_{3} =84[/tex] and
Number of ways for choosing 1 geologist from 4 [tex]=^4C_{1}= 4[/tex]
So, the total possible number of different crews they could have assembled [tex]=84*4= 336[/tex]
