Solution: The number of roots to be extracted should be greater than or equal to 0.

3a-6≥0 and 6-3a≥0

A≥2 and a≤2

So if a=2 is substituted into √(3a-6)+√(6-3a)+4=b, and b=4.

√(2a+3b)

=√(2×2+3×4)

=√(4+ 12)

=√ 16

=4