For the symbolic encoding we need 4 Boolean variables, \{$v_3$, . . . , $v_0$\}.
Let $v_3$ be the most significant bit, and $v_0$ the least significant bit.\\

(a) $s_{7}$ = $\lnot v_3 \land v_2 \land v_1 \land v_0$\\
(b) $s_{15}$ = $v_3 \land v_2 \land v_1 \land v_0$\\
(c) $s_{10}$ = $v_3 \land \lnot v_2 \land v_1 \land \lnot v_0$