Annualized active risk

Charles Griffith makes quarterly bets between stocks of industrial and utility sectors. The historical correlation between the returns of the two sectors is -0.20.Further information is as below:

Benchmark
Sector / E (R) / σ / Weight
Industrial / 12.00% / 13.0% / 80%
Utility / 5.2% / 2.5% / 20%

The annualized active risk of Griffith’s strategy is closest to:

A) 10.90%

B) 27.44%

C) 13.72%

The ans to this question is B. Their explanation to the ans is

Combined active risk = σ C = [σ I 2 -2σ I σ U r IU + σ U 2 ] 1/2

=[(0.13) ^2+( 0.025 )^2 – 2 (0.13)(0.025)(-0.20)]^ 1/2 = 0.1372 or 13.72%

Annualized active risk = 0.1372 x (4) 1/2 = 0.2744 or 27.44%

What is the rationale behind the formula and why is it divided by 1/2 in the latter part