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The exponential function
$y=400⋅0.8_{x}$
crosses the $y$-axis at the initial value $y=400,$ and is **decreasing** because the base us a decay factor of $0.8.$ The graph of this exponential function must be graph C. Read the function's value when $x=3$ in the graph.

The function's value is approximately equal to 200 when $x=3$.

b

The exponential function
$y=200⋅0.7_{x}$
cut the $y$-axis at $y=200$ and is also **decreasing** because it has a decay factor, of $0.7.$ The graph to this exponential function must be D.

The value is read to about 70 when $x=3$.

c

The exponential function

$y=400⋅1.1_{x}$
cut the $y$-axis at $y$ = 400 and is **growing** because it has a growth factor $1.1$ is greater than $1,$ which is graph B.

The function's value looks to be approximately $530$ when $x=3$.