Genetic maps of chromosomes are based on the frequency of $:-$

Define/Explain the following terms:
$1.$ Linked genes
$2.$ Locus

$A$ : In block inheritance of all genes located on the same chromosome may occur in some organisms.
$R$ : Dihybrid test cross will have only two phenotypes.

Crossing over is

There are three genes $a, b,$ and $c$. The recombination frequency between $a$ and $b$ is $20\%$,between $b$ and $c$ is $28\%$,and between $a$ and $c$ is $8\%$. What is the possible arrangement of these genes on the chromosome?

The percentage of recombination between genes $A$ and $B$ is $9\%$,between $A$ and $C$ is $17\%$,and between $B$ and $C$ is $26\%$. What is the correct arrangement of these genes on the chromosome?