Answer :

[tex]a- all\\ j-jazz\\ r_a-rap\\ r_c-rock\\\\ a=j+r_a+r_c\Rightarrow r_c=a-j-r_a\\\\ r_c=1-\frac{3}{8}-\frac{1}{4}\\\\ r_c=1-\frac{3}{8}-\frac{2}{8}\\\\ r_c=\frac{8}{8}-\frac{3}{8}-\frac{2}{8}\\\\ r_c=\frac{3}{8}[/tex]
rap - 1/4
jazz - 3/8
rock - x
all - 1


jazz + rap + rock = all

3/8 + 1/4 + x = 1
3/8 + 2/8 + x = 1
5/8 + x = 1
x = 1 - 5/8
x = 3/8

answer: rock - 3/8