The function $f$ is defined by $f(x)=a(1.8^x+1.8^b)$, where $a$ and $b$ are integer constants and $0<a<b$. The functions $g$ and $h$ are equivalent to function $f$, where $k$ and $m$ are constants. Which of the following equations displays the $y$-coordinate of the $y$-intercept of the graph of $y=f(x)$ in the $xy$-plane as a constant or coefficient?
I. $g(x)=a(1.8^x+k)$
II. $h(x)=a(1.8{)}^x+m$