Combinational Logic Circuits

answer :

X (1,2,5,6)     = A/B/C/D/ + A/B/C/D + A/BC/D/ + A/BC/D
                      = A/B/C/ ( D/ + D ) + A/BC/ ( D/ + D )
                      = A/B/C/ + A/BC/
                      = A/C/ ( B/ + B )
                      = A/C/

X (3,4,15,16) = A/B/CD + A/B/CD/ + AB/CD + AB/CD/
                      = A/B/C ( D + D/ ) + AB/C ( D + D/ )
                      = A/B/C + AB/C
                      = B/C ( A/ + A )
                      = B/C

X (12,16)       = ABCD/ + AB/CD/
                      = ACD/ ( B + B/ )   
                      = ACD/

conclusion : 
 X =    A/C/    +    B/C         +     ACD/
       (1,2,5,6)     (3,4,15,16)       (12,16)

answer :
X (1,13)   = A/B/C/D/ + AB/C/D/
                = B/C/D/ ( A/ + A )
                = B/C/D/

X (3,4)     = A/B/CD + A/B/CD/
                = A/B/C ( D + D/ )
                = A/B/C

X (5,8)     = A/BC/D/ + A/BCD/
                = A/BD/ ( C/ + C )
                = A/BD/

X (15,16) = AB/CD + AB/CD/
                = AB/C ( D + D/ )
                = AB/C

conclusion :
X = B/C/D/ + A/B/C + A/BD/ +  AB/C
       (1,13)       (3,4)      (5,8)      (15,16)

answer :
X (1,2) = A/B/C/ + A/B/C
            = A/B/ ( C/ + C )
            = A/B/

X (5,7) = ABC/ + AB/C/
            = AC/ ( B + B/ )
            = AC/

conclusion :
X = A/B/ + AC/
       (1,2)   (5,7)