Answer :
Explanation :

90 D in RA means 90 Degrees in Right Angle. It is a logic question which is to be eloborated.   Some more of its kind are: 1. 52 W in a Y     -    52 Weeks in a Year 2. 7 C in a R        -    7 Colours in a Rainbow 3. 9 P in SS 4. 5 C in an OF 5. 12 S of the Z