To find the additive inverse of the number $18$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,(18) = -18. \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ 18+(-18) = 18-18 = 0 \quad {\color{green}\checkmark} \]

The number that can be added to $12$ to give $0$ is the additive inverse of $12.$

To find the additive inverse of the number $12$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,(12) = -12. \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ 12+(-12) = 12-12 = 0 \quad {\color{green}\checkmark} \]

The number that can be added to $-17$ to give $0$ is the additive inverse of $-17.$

To find the additive inverse of the number $-17$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,(-17) = 17. \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ (-17)+17 = -17+17= 0 \quad {\color{green}\checkmark} \]

The number that can be added to $-69$ to give $0$ is the additive inverse of $-69.$

To find the additive inverse of the number $-69$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,(-69) = 69. \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ (-69)+69 = -69+69= 0 \quad {\color{green}\checkmark} \]

The number that can be added to $\dfrac{3}{8}$ to give $0$ is the additive inverse of $\dfrac{3}{8}.$

To find the additive inverse of the number $\dfrac{3}{8}$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,\left(\dfrac{3}{8}\right) = -\dfrac{3}{8} \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ \dfrac{3}{8}+\left(-\dfrac{3}{8}\right) = \dfrac{3}{8}-\dfrac{3}{8}= 0 \quad {\color{green}\checkmark} \]

To find the additive inverse of the number $-1.24$, we change its sign by placing a minus symbol $({\color{red}{-}})$ in front of it. So, we obtain

\[ {\color{red}{-}}\,(-1.24) = 1.24. \]

To check our work, we simply add the inverse to the original number. If we're correct, we should get zero.

\[ (-1.24)+1.24 = -1.24+1.24 = 0 \quad {\color{green}\checkmark} \]