Answer:
32.5 in
Step-by-step explanation:
Going up four sizes (from size 6 to size 10) requires an extra 5 in of elastic.
The rate of increase is 5 in/4 sizes or 1.25 in/size.
To increase another two sizes (from size 10 to size 12), we must add another 2 × 1.25 = 2.5 in of elastic.
The length of elastic needed for size12 is 30 + 2.5 = 32.5 in.
