The answer depends on what is meant by the "fourth term". By the binomial theorem, one answer could be

By symmetry, another could be
Answer:
30
Step-by-step explanation:
The calculation is in the image
4q-4q=8-8
0=0
None.
It doesnt has solutions
If it took Carl 30 seconds, it would take Justin 1min and 30 sec (90sec).
If it took Carl 90 seconds, it would take Justin 3min (180sec).
If it took Carl 2min, it would take Justin 6min (360sec).