Answer
You need 210 in of string to make a 15 in long necklace.
Work Step by Step
using the equation y=2x+180 we can find the amount of string needed to create a 15 in ling necklace.
x=15 as necklace length independent variable
y=2(15)+180
y=30+180
y=210
Therefore, 210 inches of string required to make a 15 in long necklace.