Help does anyone know im having trouble

An energy drink company claims that its product increases students' memory levels. to support its claims, the company issues advertisements claiming that 8 out of 10 people (chosen randomly from across the country) who tried their product reported improved memory. the missing component in this study is a .

Answer for 10 points show work you guys in advanced < 3

Awasher and a dryer cost $701 combined. the washer costs $51 more than the dryer. what is the cost of the dryer?