Adrum set originally costs $500, but it is on sale for 20% off. if a customer buying the drum set has a $70 gift card, what will her final price be on the drum set?

20% of $500 is $100, so you take away $100 from $500.
  =   500 - 100 

This leaves you $400. When the customer buys the drum set, you take $70 off of $400;

400 - 70 
which leaves you with $330 as the final price. 

Step 1: 6x-10=1; step 2: 6x=11

I’m pretty sure the answer is a