(a) Recombination frequencies are made by crossing homozygous recessive (for both genes) individuals with heterozygous individuals and looking for recombinant phenotypes (this is basically a test cross for 2 genes at once). The percentage of recombinants gives the recombination frequency and the map distance. (b) Please see the image for the map.
Work Step by Step
The map is produced by playing with the various pairwise distances until an overall map is found which fits them all--it's like doing a puzzle in which the pieces vary by length, using trial-and-error.