Twice the difference between 6 times h and 3 gives 30

How is this equation completed? i cannot find any examples in the book.

Lauren has five shells she found on the beach seashells represent one-third of the shells her whole collection how many shells does lauren have in her whole collection

Asalesperson set a goal to earn $2,500 in august. she receives a base salary of $1,000 per month as well as a 20% commission for all sales in that month. how many dollars of merchandise will she have to sell to meet her goal?