If it were 

jA-10A

then you would factor out the red A, and it would
leave the green j and the green -10
to go in black parentheses like this:

A(j-10) 

Therefore since it's

j(k-5)-10(k-5)

then you likewise factor out the red (k-5), and it
leaves the green j and the green -10 
to go in black parentheses like this:

(k-5)(j-10)

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The only difference is that A doesn't take up
as much space as (k-5).  One thing to learn in
algebra is how to treat big chunks of algebra the 
same way as you treat little chunks of algebra.

Edwin