Who used the frequency of recombination as a measure of the distance between genes on a chromosome and mapped their position?

In a fruit fly,the $X$-chromosome linkage map has a total length of $66$ units,with the yellow body gene $(y)$ at one end and the bobbed hair gene $(b)$ at the other end. What will be the recombination frequency between these two genes $(y$ and $b)$?

The distance between two linked genes on a chromosome is measured in cross-over units,which is:

If the gene exchange rate (recombination frequency) of two linked genes is $30\%$,then the distance between these two genes is:

. . . . . . $(B)$ . . . . . . used the frequency of recombination between gene pairs on the . . . . . . $(A)$ . . . . . . as a measure of the distance between genes and mapped their position on the chromosome.
$(A) \quad\quad (B)$

There are three genes $a, b,$ and $c$. The percentage of crossing over between $a$ and $b$ is $20\%$,between $b$ and $c$ is $28\%$,and between $a$ and $c$ is $8\%$. What is the sequence of these genes on the chromosome?