#### Answer

$B(t)=4.0+0.35 sin[\frac{2π}{5.4} t]$

#### Work Step by Step

The average brightness is 4.0.
The amplitude of the graph is 0.35.
The period is 5.4 days.
We can use these values to write a function that models the brightness:
$B(t)=4.0+0.35 sin[\frac{2π}{5.4} t]$