<PRE><B>Question 774165</B>
Use x for the $5 size and y for the $20 size count of each bill type.

{{{5x+20y=75}}} and you want only whole number possibilities.
Simplify...{{{x+4y=15}}}

The count of x should be more than the count of y, so you could just solve the equation for y, and check the whole number results for x values starting at 1.  Some will work and some will fail.


The easier way to do this is start with {{{75/5=15}}} of the $5 bills, and successively step-wise subtract $20 value as 4 of the $5 bills until no more can be substituted.


Each
Bill
Count____$5______$20
------------------------------
_________15______0
_________11______1
_________7_______2
_________3_______3</PRE>