A  = 1
2 × (15 + 20) × 16
B  = 1
2 × 15 × 20 × 10
C  = 1
2 × (15 + 20) × 10
D  = 1
2 × (10 + 16) × 20
                                             
                                          
                                          
                                        
											 
			                  