First: solve the expressions
(a) 50% of 20= (.50*20)=10
(b) 30% of 90= (.30*90)=27
(c) 25% of 80= (.25*80)= 20
Next: use substitution
(a) 2(10)=(27) (this is not true)
(b) (27)-(10)=(20) (this is not true)
(c) (10)+(20)=(27) (this is not true)
(d) 2(10)=(20) (this is true)
Your answer is D. Hope this helps :)