Answer:
 Beta of Stock C is 1.6
correct option is d. 1.6
Step-by-step explanation:
given data 
portfolio beta = 1.2
stock A beta = 0.9
stock B beta = 1.1
to find out 
beta of stock C
solution
we will apply here Portfolio Beta equation that is express as 
Portfolio Beta = ( Weight of Stock A × Beta of Stock A ) + ( Weight of Stock B × Beta of Stock B ) + ( Weight of Stock C × Beta of Stock C ) ......................1
here weight for each stock = 

 put here value we will get 
1.2 = ( 
 × 0.9 ) + (
 × 0.9 ) + ( 
 × 1.1 ) + (
 × 1.1 ) + ( 
 × Beta of Stock C )
 × Beta of Stock C ) 
solve it we will get 
Beta of Stock C = 1.599
 so Beta of Stock C is 1.6
and correct option is d. 1.6