Answer
$\text{exponential growth}$;
$y$-intercept = $3$
Work Step by Step
RECALL:
The exponential function $y=c \cdot b^x$ represents:
(1) an exponential growth when $b\gt 1$.
(2) an exponential decay when $0\lt b \lt 1$.
The given exponential function has $b=5$, which is greater than $1$.
Thus, the exponential function represents an exponential growth.
The $y$-intercept can be found by setting $x=0$ then solving for $y$:
\begin{align*}
f(x)&=3(5^x)\\
f(0)&=3(5^0)\\
f(0)&=3(1)\\
f(0)&=3
\end{align*}
Therefore, the $y$-intercept is $3$.
