In this question we can find all the necessary information's are already provided. By using those information's it is possible to find the required answer. It is given that Mae Ling has a weekly salary of $330 and it is fixed. The variable part is the commission she gets on the sales she does. She sold gooods worth $4200 in the week. She earns a commission of 6.5% on the sales.
Now
Amount of commission Mae Ling makes in the week = 4200 * (6.5/100) dollars
= 273 dollars
So the total amount earned by Mae Ling in the work week = (330 + 273) dollars
= 603 dollars