To get from 17 to 9, you would divide by 17 and then multiply by 9, so in order to find y, you would multiply 7 by 9/17:
7 * 9/17
= 63/17
Now, you just have to simplify. That could be written as 3 12/17 if you turn it into a proper fraction, or if you turn it into a decimal, you would get about 3.71 (rounding to the tenths).