Answer:
 Total earnings of Ruby for the month is $4020 . 
Option (d) is correct . 
Explanation:
As given 
Ruby has a monthly salary of $1,800 and also earns 6% commission on her sales. 
If Ruby had $37,000 in sales last month . 
6% is written in the decimal form 

= 0.06 
Equation becomes 
Total earnings for the month = Monthly salary + 0.06 × Sales last month 
Put all the values in the above 
 = 1800 + 0.06 × 37000
 = 1800 + 2220
 = $ 4020 
Therefore the total earnings of Ruby for the month is $4020 . 
Option (d) is correct .