Question 44415
D=2M  M=B-4 & B=D-17 THEN B=2M-17 & B=M+4 OR M+4=2M-17 OR 21=M THUS 

21=B-4 OR B=21+4 OR B=25 THEN D=2*21 OR D=42

42=2*21 OR 42=42
21=25-4 OR 21=21
25=42-17 OR 25=25