Question 893781
Suppose she works X hours in a week.

According to question, if x < 40
$20 per hour for the first 40 hours 
hence Total earnings F(x) = 20 X

If X>40
$20 per hour for the first 40 hours 
Hence earnings for the first 40 hours= 20*40 = $800

Total earnings F(x)= 800 + 30(X-40)