The relation is \
\
x \ | \
\
y \ | \
\
15 \ | \
\
7 \ | \
\
20 \ | \
\
12 \ | \
\
21 \ | \
\
13 \ | \
\
30 \ | \
\
22 \ | \
\
42 \ | \
\
34 \ | \
Observe the table and write a rule
\ \ \
The function is .