Answer
$z=e^x$
Work Step by Step
When projecting to the xz plane, only the x and z components have to be considered. The $x$ and $z$ components of $r(t)$ are $x(t)=t$ and $z(t)=e^t$, respectively. Substituting $x(t)$ in for $t$ gives $z(t)=e^{x(t)}$, which can be written as $z=e^x$.
