Pls answer the question in the picture!!! I NEED HELP
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The Empire is attacking a Rebel base that is stocked with X-wings and
Y-wings. The Rebels need to build a fleet consisting of
ships (with at least 1 X-wing), to be led by 1 pilot in an X-wing.
There are ways of picking the leader, and
ways of building the rest of the fleet, so there's a total of
ways of building such a fleet.
In the other direction, suppose we build a fleet comprising of X-wings and
Y-wings. We have
ways of picking X-wings and
ways of picking Y-wings. Also from the
X-wings we pick 1 to be the leader, which we can do in
ways. So there are
ways of building such a fleet. But since
, we have
ways of building the fleet with these specifications. Sum over all possible values of ,
interesting puzzle,
total CDs=
country CDs $c$ is half of rock CDs $r$, $r=2c$
and one fourth of soundtrack $s$ as country CDs , $c=4s$
express in common variable s, $r+c+s=39$
$2(4s)+4s+s=39 \implies s=3$
so $c=12$ and $r=24$
after borrowing 3 rock CDs, there be $21$ rock CDs rest will be same