For this case we have the following equation:
s = root (S.A / 6)
Substituting values we have:
For S.A = 180:
s = root (180/6)
s = root (30)
For S.A = 120:
s = root (120/6)
s = root (20)
s = root (4 * 5)
s = 2 * root (5)
Subtracting both values we have:
root (30) - 2 * root (5)
Answer:
root (30) - 2 * root (5)
option 2