She can make 18 rings using the string she bought.
We simply divide 144 centimeters by 8 centimeters to get the number of strings that can make the rings.
144 / 8 = 18 cm strings.
If you want to know the direct variation equation. then:
y = 8x where y is the total number centimeters to be bought; x is the number of rings to be made; while 8 is the constant of variation because 1 ring is made up of 8 cm of string.
