Recombinant Frequency SNP markers: monohybrid ?

Hi

 I am curious to know how calculate recombinant frequency for monohybrids ( three point link, gene map etc.)

Here is an example based SNP calls ( xx=parent 1, yy= parent 2) with three markers (M1, M2, M3) these are hypothetical  SNP calls.

Marker 1

    xx= 10
    xy=20
    yy= 5

Marker 2

    xx=30
    yx= 10
    yy= 10

Marker 3

    xx= 20
    yx=40
    yy= 10

This is what I think it would be like for x:x Marker 1 to 3

grand total = 155

This how I have been doing it for now

M1 to M2 :

xy = 30/155 =19.35%

xx= 40/155= 25.81%

15/155= 9.67%

This is not a problem from a textbook or anything  I made this up from the top my head.

Am I on the right track --- if not can you please show how it would be done for this example?