What function can i use to determine a value from a range?

A B c
0 300 0.6
301 600 0.8
601 900 1.0
901 1200 1.2


So if i have a value of 500, it will compare between A & B, to provide a
value C. in this case 0.8.

Can someone advise me the best way to achieve this?

I have already generated a VLOOKUP for columns B & C, but not sure how to
get a value that is between A and B.

Thanks.