Answer
$31,438\text{ units}$.
Work Step by Step
(b) For February 2018, $t=2+12=14$.
Substitute $t=14$ into the equation:
$$S=23.1+0.442(14)+4.3\cos \left(\frac{\pi(14)}{6}\right)=31.438$$
The predicted sales are then:
$$31.438(1000)=~31,438\text{ units}$$
