[tex]\displaystyle \\
x+21=35 \\
x = 35 - 21 = \boxed{14} \\ \\ \\
3x+1 \ \textless \ 32,02 \\
3x \ \textless \ 32,02-1 \\
3x \ \textless \ 31,02 \\ \\
x\ \textless \ \frac{31,02}{3} \\ \\
x\ \textless \ 10,34 ~~~~~si ~~~~~ x \in N \\
\boxed{x\in \{0;~1;~2;~3;~4;~5;~6;~7;~8;~9;~10\} }[/tex]