An electrical contractor's records during the last five weeks indicate the number of job requests:

Week

$1$

$2$

$3$

$4$

$5$

Requests

$20$

$22$

$18$

$21$

$22$

Predict the number of requests for week $6$ using each of these methods:

a$.$ Naive

b$.$ A four$-$period moving average

c$.$ Exponential smoothing with $=30$; use $20$ for week $2$ forecast