Hexadecimal Equations (Problem $1$ )

$D = 13$

$2 \times 16^1 = 32$

$9 \times 16^1 = 144$

$32 + 144 + 13 + 13$

$32 + 144 + 26$

$58 + 144$

$8 + 194$

$202$

Answer $\rightarrow \fbox{202}$

For the Bonus:

$202$

Do division by $16$ to get the L.H.S of the modulo calculations.

$202 (\text{mod}(16)) = 10$

$12 (\text{mod}(16)) = 12$

Read the remainders from bottom to top:

$1210$

Since $12 = C, 10 = A$ :

$CA$

Bonus Answer $\rightarrow CA$