If ‘a’ Means ‘x’ ; ‘b’ Means ‘¸’ ; ‘c’ Means ‘+’ and ‘d’ Means ‘-‘, then Calculate:

If ‘a’ means ‘x’ ; ‘b’ means ‘¸’ ; ‘c’ means ‘+’ and ‘d’ means ‘-‘, then calculate;
21c 3d 6a 8b2.

1. 48
2. 13
3. 0
4. 72