[tex]\it a) 121_{(3)} = 3^2+2\cdot3+1 = 9+6+1 = 16
\\\;\\
x_{(4)} = 16_{(10)}
\\\;\\
16 = 4^2 = 100_{(4)} \Longrightarrow x = 100
[/tex]
[tex]\it \ b ) \ 34_{(5)} =3\cdot5+4 = 19_{(10)}
\\\;\\
19_{(10)} =x_{(2)},\ \ \ x = ?
\\\;\\
19 = 2^4+2+1 = 10011_{(2)} \Longrightarrow x = 10011
[/tex]
[tex]\it c)\ \ 110011_{(2)} = 2^5+2^4+2+1 = 32+16+2+1= 51_{(10)}[/tex]