Three years ago, ava lent her sister $400 to buy some clothes. today ava’s sister paid her loan in full with $454. what simple annual interest rate did she pay?

Ava's sister paid a 4.5% annual interest rate

Her sister paid $54 more than she borrowed, divide that by 3 (years till she paid)

54/3 = 18

That's $18 for every year she'd had the $400 loan out, divide it by 4 to get the percentage 

18/4 = 4.5/100 = 4.5%