#### Answer

Converse: If $2x-5=19$, then $x=12$.
Biconditional: $x=12$ if and only if $2x-5=19$.

#### Work Step by Step

To write the converse of a conditional statement, write a new conditional statement that switches the hypothesis and conclusion.
To write a biconditional, join the hypothesis and the conclusion with the term "if and only if".