Let us assume the number of times Nicolas skydived = x
Then
Number of times Gus skydived = x + 4
Number of times Emma skydived = 2x
It is also given that the number of times Emma skydived = 16
So
2x = 16
x = 8
So the number of times Gus skydived = x + 4
= 8 + 4
= 12
So the total number of times Gus skydived is 12. I hope the procedure for solving this problem is clear to you and in future you can do such problems on your own.