Please help me with 5 and 7

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 .

I’m stuck on this equation, anyone got the answer?

How do i put 3(x+7) in distributive property