Answer
The function would be y=2x+180 as the amount of string would be dependent on the necklace length.
The graph of function is shown below.
Work Step by Step
The equation was created using system of equation.
y=mx+b. 2 points-->(10,200) (11,202)
1. (200=10m+b) $\times$-1
2. 202=11m+b.
-200=-10m-b
2=m
200=2(10)+b
200=20+b
b=180
Therefore the function rule is
y=2x+180
