trying to figure out bc my math teacher is strict and i don't wanna get something wrong

Question

Michelle has a starting balance on a gift card for $300. she buys several dresses at $40 a peice. after her purchases she has $140 left on the gift card. how many dresses did she buy?

Answer 1

d represents the number of dresses she purchased

$300 - $40d = $140

 

Can you solve for d?