Can you break down the solution for me for this math problem: Morgan's dad said that she had $90 budgeted for her birthday party. She wants to make sure she and her friends all get to play one round of mini-golf, have $5 in arcade tokens, and get to ride the go-karts twice. A round of mini-golf is $5. The Go-karts cost $10 a ride. How many friends can she invite?