Answer:
6210
Step-by-step explanation:
This is simple problem of section of few things from a lot.
[tex]A_{1}[/tex]: selection of 4 shirts from 15 shirts
[tex]A_{2}[/tex]: selection of 4 shirts from 20 shirts
[tex]A_{1}[/tex] = [tex]\binom{15}{4}= \frac{15!}{4!\times11!}[/tex]
=1365
[tex]A_{2}[/tex] = [tex]\binom{20}{4}= \frac{20!}{4!\times16!}[/tex]
=4845
so the number of ways in which she can select shirts
= 1365+4845= 6210
