a)
[tex]2^7+2^6+2^4+2^3+2^0=128+64+16+8+1=217[/tex]
[tex]11011001_2=217_{10}[/tex]
b)
6651/2=3325r1
3325/2=1662r1
1662/2=831r0
831/2=415r1
415/2=207r1
207/2=103r1
103/2=51r1
51/2=25r1
25/2=12r1
12/2=6r0
6/2=3r0
3/2=1r1
1/2=0r1
[tex]6651_{10}=1100111111011_2[/tex]
c)
[tex]\text{D}=13\\\text{E}=14\\\\13\cdot16^3+14\cdot16^2+7\cdot16^1+13\cdot16^0=53248+3584+112+13=56957\\\text{DE$7$D}_{16}=56957_{10}[/tex]
d)
549/16=34r5
34/16=2r2
2/16=0r2
[tex]549_{10}=225_{16}[/tex]